diff --git a/just-responsive-images.php b/just-responsive-images.php
index f207be2..81daf0c 100644
--- a/just-responsive-images.php
+++ b/just-responsive-images.php
@@ -4,7 +4,7 @@
 Plugin Name: Just Responsive Images
 Description: Providing full control to set your own responsive image properties for WordPress 4.4+, the ability to use the <picture> tag, auto-generate image backgrounds and supports retina images.
 Tags: responsive post thumbnail, post thumbnail as background, retina support, retina image, retina post thumbnail, responsive post attachment, responsive images, responsive attachments, post thumbnails, media
-Version: 1.5.1
+Version: 1.6.0
 Author: JustCoded / Alex Prokopenko
 Author URI: http://justcoded.com/
 License: GPL3
@@ -49,7 +49,7 @@ class JustResponsiveImages extends core\Singleton {
 	protected function __construct() {
 		// init plugin name and version.
 		self::$plugin_name = __( 'Just Responsive Images', JustResponsiveImages::TEXTDOMAIN );
-		self::$version     = '1.501';
+		self::$version     = '1.600';
 
 		// init features, which this plugin is created for.
 		new components\Maintenance();
diff --git a/models/RwdImage.php b/models/RwdImage.php
index 08925b9..aaaa36e 100644
--- a/models/RwdImage.php
+++ b/models/RwdImage.php
@@ -80,6 +80,7 @@ class RwdImage {
 	 * @param \WP_Post|int|null $attachment Image attachment to be displayed.
 	 */
 	public function __construct( $attachment ) {
+		defined( 'JRI_DUMMY_IMAGE' ) || define( 'JRI_DUMMY_IMAGE', false );
 		$this->attachment = $this->load_attachment( $attachment );
 	}
 
@@ -98,10 +99,11 @@ public function verify_svg_mime_type( $attachment ) {
 		}
 	}
 
+
 	/**
 	 * Generate <picture> tag for the current attachment with specified size
 	 *
-	 * @param string|array $size       Required image size.
+	 * @param string|array $size Required image size.
 	 * @param array        $attributes Additional html attributes to be used for main tag.
 	 *
 	 * @return string
@@ -154,16 +156,20 @@ public function picture( $size, $attributes = array() ) {
 				$meta_data = $this->get_attachment_metadata( $sources[ $subkey ]['attachment_id'] );
 				$baseurl   = $this->get_attachment_baseurl( $sources[ $subkey ]['attachment_id'] );
 
-				$src = array( $baseurl . $sources[ $subkey ]['file'] );
+				$src = array(
+					$this->get_attachment_url( $baseurl, $sources[ $subkey ] ),
+				);
 				// get retina sources.
 				if ( $option->retina_options ) {
 					foreach ( $option->retina_options as $retina_descriptor => $multiplier ) {
 						$retina_image_size = ImageSize::get_retina_key( $option->key, $retina_descriptor );
 						if ( ! empty( $meta_data['sizes'][ $retina_image_size ] ) ) {
-							$src[] = $baseurl . $meta_data['sizes'][ $retina_image_size ]['file'] . ' ' . $retina_descriptor;
+							$src[] = $this->get_attachment_url( $baseurl, $meta_data['sizes'][ $retina_image_size ] )
+									. ' ' . $retina_descriptor;
 						}
 					}
 				}
+
 				$tokens = array(
 					'{src}'        => esc_attr( implode( ', ', $src ) ),
 					'{alt}'        => $attr['alt'],
@@ -172,7 +178,7 @@ public function picture( $size, $attributes = array() ) {
 				);
 
 				$template = $option->picture ? $option->picture : $default_template;
-				$html .= strtr( $template, $tokens ) . $this->eol;
+				$html    .= strtr( $template, $tokens ) . $this->eol;
 			}
 			$html .= '</picture>';
 		} // End if().
@@ -185,7 +191,7 @@ public function picture( $size, $attributes = array() ) {
 	/**
 	 * Generate <img> tag for the current attachment with specified size
 	 *
-	 * @param string|array $size       Required image size.
+	 * @param string|array $size Required image size.
 	 * @param array        $attributes Additional html attributes to be used for main tag.
 	 *
 	 * @return string
@@ -220,23 +226,27 @@ public function img( $size, $attributes = array() ) {
 				if ( ! isset( $sources[ $subkey ] ) || is_null( $option->srcset ) ) {
 					continue;
 				}
+
 				$baseurl   = $this->get_attachment_baseurl( $sources[ $subkey ]['attachment_id'] );
 				$meta_data = $this->get_attachment_metadata( $sources[ $subkey ]['attachment_id'] );
 
 				$tokens = array(
-					'{src}' => esc_attr( $this->get_attachment_baseurl( $sources[ $subkey ]['attachment_id'] ) . $sources[ $subkey ]['file'] ),
+					'{src}' => esc_attr( $this->get_attachment_url( $baseurl, $sources[ $subkey ] ) ),
 					'{w}'   => $meta_data['sizes'][ $option->key ]['width'],
 				);
+
 				// get retina sources.
 				if ( $option->retina_options ) {
 					foreach ( $option->retina_options as $retina_descriptor => $multiplier ) {
 						$retina_image_size = ImageSize::get_retina_key( $option->key, $retina_descriptor );
 						if ( ! empty( $meta_data['sizes'][ $retina_image_size ]['width'] ) ) {
 							$retina_width = $meta_data['sizes'][ $retina_image_size ]['width'];
-							$srcset[]     = $baseurl . $meta_data['sizes'][ $retina_image_size ]['file'] . ' ' . $retina_width . 'w';
+							$srcset[]     = $this->get_attachment_url( $baseurl, $meta_data['sizes'][ $retina_image_size ] )
+											. ' ' . $retina_width . 'w';
 						}
 					}
 				}
+
 				$src      = $tokens['{src}'];
 				$srcset[] = strtr( "{src} $option->srcset", $tokens );
 				if ( $option->sizes ) {
@@ -269,7 +279,7 @@ public function img( $size, $attributes = array() ) {
 	 * Generate background media queries
 	 *
 	 * @param string       $selector CSS selector.
-	 * @param string|array $size     Required image size.
+	 * @param string|array $size Required image size.
 	 *
 	 * @return string Generated html comments warnings.
 	 */
@@ -288,13 +298,13 @@ public function background( $selector, $size ) {
 			}
 			// generation of responsive sizes.
 			foreach ( $rwd_options as $subkey => $option ) {
-				if ( ! isset( $sources[ $subkey ] ) || is_null( $option->bg ) ) {
+				if ( ! isset( $sources[ $subkey ] ) || is_null( $option->srcset ) ) {
 					continue;
 				}
 				$baseurl   = $this->get_attachment_baseurl( $sources[ $subkey ]['attachment_id'] );
 				$meta_data = $this->get_attachment_metadata( $sources[ $subkey ]['attachment_id'] );
 
-				$src   = $this->get_attachment_baseurl( $sources[ $subkey ]['attachment_id'] ) . $sources[ $subkey ]['file'];
+				$src   = $this->get_attachment_url( $baseurl, $sources[ $subkey ] );
 				$media = str_replace( '{w}', $meta_data['sizes'][ $option->key ]['width'], $option->bg );
 
 				if ( ! isset( $rwd_background_styles[ $media ] ) ) {
@@ -312,7 +322,7 @@ public function background( $selector, $size ) {
 						$retina_image_size = ImageSize::get_retina_key( $option->key, $retina_descriptor );
 
 						if ( ! empty( $meta_data['sizes'][ $retina_image_size ] ) ) {
-							$src_retina   = $baseurl . $meta_data['sizes'][ $retina_image_size ]['file'];
+							$src_retina   = $this->get_attachment_url( $baseurl, $meta_data['sizes'][ $retina_image_size ] );
 							$media_retina = strtr( $option->bg_retina, array(
 								'{dpr}'     => "(-webkit-min-device-pixel-ratio:{$media_pixel_ration})",
 								'{min_res}' => "(min-resolution : {$media_resolution})",
@@ -333,7 +343,7 @@ public function background( $selector, $size ) {
 	/**
 	 * Generate img tag for svg image
 	 *
-	 * @param string|array $size       Required image size.
+	 * @param string|array $size Required image size.
 	 * @param array        $attributes Image attributes.
 	 *
 	 * @return string Generated html comments warnings.
@@ -342,7 +352,7 @@ public function svg( $size, $attributes ) {
 
 		// prepare image attributes (class, alt, title etc).
 		$attr = array(
-			'class' => "wp-post-image",
+			'class' => 'wp-post-image',
 			'alt'   => trim( strip_tags( get_post_meta( $this->attachment->ID, '_wp_attachment_image_alt', true ) ) ),
 		);
 
@@ -415,7 +425,6 @@ public function get_set_sources() {
 		if ( empty( $this->rwd_set ) ) {
 			return null;
 		}
-
 		$sources           = array();
 		$attachment_meta   = $this->get_attachment_metadata( $this->attachment->ID );
 		$is_attachment_svg = $this->verify_svg_mime_type( $this->attachment );
@@ -426,6 +435,8 @@ public function get_set_sources() {
 				$attachment_meta['sizes'][ $this->rwd_set->key ]['width'] : $attachment_meta['width'];
 		}
 
+		$dummy_sizes = array();
+		$dummy_meta  = array();
 		foreach ( $this->rwd_set->options as $subkey => $option ) {
 			$attachment     = empty( $this->rwd_rewrite[ $subkey ] ) ? $this->attachment : $this->rwd_rewrite[ $subkey ];
 			$meta_data      = $this->get_attachment_metadata( $attachment->ID );
@@ -433,7 +444,6 @@ public function get_set_sources() {
 
 			// svg images doesn't have meta data, so we need to generate it.
 			if ( $is_subsize_svg ) {
-
 				if ( ! is_array( $meta_data ) ) {
 					$meta_data = array();
 				}
@@ -462,21 +472,38 @@ public function get_set_sources() {
 					$option->size->h,
 					$option->size->crop
 				);
+				if ( JRI_DUMMY_IMAGE && empty( $meta_data['sizes'][ $option->key ]['file'] ) ) {
+					$dummy_sizes[ $option->key ] = $this->dummy_source( $option, false, $meta_data );
+				}
+
 				// Resize retina images if not exists.
 				if ( $option->retina_options ) {
 					foreach ( $option->retina_options as $retina_descriptor => $multiplier ) {
-						$meta_data = $this->resize_image(
+						$retina_image_size = ImageSize::get_retina_key( $option->key, $retina_descriptor );
+						$meta_data         = $this->resize_image(
 							$attachment->ID,
 							$meta_data,
-							ImageSize::get_retina_key( $option->key, $retina_descriptor ),
+							$retina_image_size,
 							$option->size->w * $multiplier,
 							$option->size->h * $multiplier,
 							$option->size->crop
 						);
+
+						if ( JRI_DUMMY_IMAGE && empty( $meta_data['sizes'][ $retina_image_size ]['file'] ) ) {
+							$dummy_sizes[ $retina_image_size ] = $this->dummy_source( $option, $multiplier, $meta_data );
+						}
 					}
 				}
 			}
 
+			if ( JRI_DUMMY_IMAGE ) {
+				if ( ! isset( $dummy_meta[ $attachment->ID ] ) ) {
+					$dummy_meta[ $attachment->ID ] = $meta_data;
+				}
+				$meta_data['sizes'] = array_merge( $dummy_meta[ $attachment->ID ]['sizes'], $dummy_sizes );
+				$dummy_meta[ $attachment->ID ] = $meta_data;
+			}
+
 			// however if we didn't find correct size - we skip this size with warning.
 			if ( ! isset( $meta_data['sizes'][ $option->key ] ) ) {
 				$this->warnings[] = "Attachment {$attachment->ID}: missing image size \"{$this->rwd_set->key}:{$subkey}\"";
@@ -487,18 +514,67 @@ public function get_set_sources() {
 			$sources[ $subkey ]['attachment_id'] = $attachment->ID;
 		} // End foreach().
 
+		// cache all dummy retina sizes to get correct width/height options for retina.
+		if ( JRI_DUMMY_IMAGE ) {
+			foreach ( $dummy_meta as $attachment_id => $meta_data ) {
+				$this->set_attachment_metadata( $attachment_id, $meta_data );
+			}
+		}
+
 		return $sources;
 	}
 
+	/**
+	 * Generate generate fake src for empty image sizes
+	 *
+	 * @param RwdOption $option empty image size options.
+	 * @param int|bool  $retina_multiplier retina multiplier for retina size.
+	 * @param array     $meta_data image attachment WP metadata.
+	 *
+	 * @return string
+	 */
+	public function dummy_source( $option, $retina_multiplier = false, $meta_data = false ) {
+
+		$sizename = $option->key;
+
+		$w = $option->size->w;
+		$h = $option->size->h;
+
+		$ratio = null;
+		if ( ! empty( $meta_data['width'] ) && ! empty( $meta_data['height'] ) ) {
+			$ratio = $meta_data['width'] / $meta_data['height'];
+		}
+
+		if ( is_null( $h ) || 9999 === $h ) {
+			$h = $ratio ? floor( $w / $ratio ) : $w;
+		} elseif ( is_null( $w ) || 9999 === $w ) {
+			$w = $ratio ? floor( $h * $ratio ) : $h;
+		}
+
+		if ( $retina_multiplier ) {
+			$w *= $retina_multiplier;
+			$h *= $retina_multiplier;
+		}
+
+		$color     = substr( md5( "{$meta_data['file']}-$w-$h" ), 0, 6 );
+		$dummy_url = "http://via.placeholder.com/{$w}x{$h}/$color";
+
+		return [
+			'file'   => $dummy_url,
+			'width'  => $w,
+			'height' => $h,
+		];
+	}
+
 	/**
 	 * Dynamically resize image.
 	 *
 	 * @param int    $attach_id Attachment ID.
 	 * @param array  $meta_data Attachment meta data.
-	 * @param string $key       Image size key.
-	 * @param int    $width     Image width.
-	 * @param int    $height    Image height.
-	 * @param int    $crop      Crop image.
+	 * @param string $key Image size key.
+	 * @param int    $width Image width.
+	 * @param int    $height Image height.
+	 * @param int    $crop Crop image.
 	 *
 	 * @return array
 	 */
@@ -512,6 +588,11 @@ public function resize_image( $attach_id, $meta_data, $key, $width, $height, $cr
 			|| $meta_data['sizes'][ $key ]['rwd_width'] !== $width || $meta_data['sizes'][ $key ]['rwd_height'] !== $height
 			|| ( 0 !== strcmp( $crop_str, $meta_data['sizes'][ $key ]['crop'] ) )
 		) {
+			// in dummy mode we do not resize anything.
+			if ( JRI_DUMMY_IMAGE ) {
+				return $meta_data;
+			}
+
 			// Get WP Image Editor Instance.
 			$image_path   = get_attached_file( $attach_id );
 			$image_editor = wp_get_image_editor( $image_path );
@@ -562,7 +643,7 @@ public function resize_image( $attach_id, $meta_data, $key, $width, $height, $cr
 				$this->set_attachment_metadata( $attach_id, $meta_data );
 				// update metadata.
 				wp_update_attachment_metadata( $attach_id, $meta_data );
-				// update JIO attachment status
+				// update JIO attachment status.
 				update_post_meta( $attach_id, '_just_img_opt_status', self::STATUS_IN_QUEUE );
 			}
 		}
@@ -630,7 +711,7 @@ protected function get_attachment_metadata( $attachment_id ) {
 	 * Set updated values to cache
 	 *
 	 * @param int   $attachment_id Attachment post to update it's metadata cache.
-	 * @param array $meta_data     New meta data values.
+	 * @param array $meta_data New meta data values.
 	 */
 	protected function set_attachment_metadata( $attachment_id, $meta_data ) {
 		static::$meta_datas[ $attachment_id ] = $meta_data;
@@ -666,6 +747,23 @@ protected function get_attachment_baseurl( $attachment_id ) {
 		return static::$base_urls[ $attachment_id ];
 	}
 
+	/**
+	 * Generate final file URL.
+	 *
+	 * @param string $baseurl Attachment folder base url.
+	 * @param array  $source File sources array.
+	 *
+	 * @return string
+	 */
+	protected function get_attachment_url( $baseurl, $source ) {
+		$url = $source['file'];
+
+		if ( ! preg_match( '/^http/', $url ) ) {
+			$url = $baseurl . $url;
+		}
+		return $url;
+	}
+
 	/**
 	 * Alias for global variable to simlify code.
 	 *
diff --git a/readme.txt b/readme.txt
index a5e1fef..5364ef4 100644
--- a/readme.txt
+++ b/readme.txt
@@ -6,7 +6,7 @@ Tags: responsive post thumbnail, post thumbnail as background, retina support, r
 Author: JustCoded / Alex Prokopenko
 Author URI: http://justcoded.com/
 Requires at least: 4.5
-Tested up to: 4.9.4
+Tested up to: 4.9.6
 Requires PHP: >=5.6
 License: GPL3
 Stable tag: trunk
@@ -40,6 +40,14 @@ Our plugin resize images ONLY when you open the page with an image, printed with
 In version 1.2 default RWD set background options updated to mobile-first strategy (from desktop-first).
 If you use nested rules from RWD set you should update your main size background option to have @media query with `min-width` rule.
 
+= DEV Mode =
+
+In DEV mode plugin does not resize any images and simply use placeholder images. This can be used to reduce disk space, while you develop and configure our plugin to match all required screen sizes.
+
+To enable it you need to define new constant in your wp-config.php file:
+
+`define( 'JRI_DUMMY_IMAGE', true );`
+
 == Installation ==
 
 1. Download, unzip and upload to your WordPress plugins directory
@@ -82,6 +90,8 @@ There are no any special upgrade instructions for version 1.0 - 1.3
 To upgrade remove the old plugin folder. After than follow the installation steps 1-2.
 
 == Changelog ==
+= Version 1.6.0 - 27 June 2018 =
+    * Dev mode with placeholder images instead of real images in case correct sizes are missing. 
 = Version 1.5.1 - 3 April 2018 =
     * Added compatibility with Crop Images plugin
     * Fix main editor content responsive images (it was broken after some WP update)