You are probably missing ImageMagick (PHP extension). Install it and the JPG artifacts will be gone.
Related Posts:
- Dynamically determine the width and height of a image file to be cropped & uploaded AFTER form submission given fixed aspect ratio
- get the post thumbnail returns the full size
- No Thumbnails Generated
- Is there a hook which fires after all thumbnails are generated?
- Settings in ‘Media > Settings’ is ignored when inserting images
- Convert uploaded PNG to JPEG automatically
- Regenerate thumbnails unexpected resolution (96 x 96)
- add_image_size() and uploading the exact size leaves 1×1 image in uploads
- How to stop thumbnail generation from some images and different size thumbnail generate
- Can’t generate thumbnail images
- Original image not saving?
- How to Make Thumbnail of Post Stay Animated
- adding image to post thumbnail from another server
- WordPress Multisite: Images moved to /sites/1?
- Redimension thumbnail crop without creating new images
- WordPress pointing animated GIF images with wrong file name upon upload (GIFs animation not working)
- How does WP media uploader create the 3 different sized images, and how can I duplicate it
- How to disable generation of default image sizes for some custom post types?
- Reject upload of wrong-sized images using the Media Uploader
- Upload post thumbnail from the front end
- Download an image from a webpage to the default uploads folder
- Create image formats with different qualities when uploading
- Which filters or actions to use after a media upload and delete?
- get_the_post_thumbnail_url with an unregistered size
- Cropped featured image replaces original image in gallery
- How to prevent upload of a multiple sizes of images
- Impose a Maximum Limit on Image height and width upload size
- Force wordpress to see uploads folder media
- add_image_size creating lots of images (of various sizes)
- How can I add the “Use as featured image” to a custom metabox?
- Can WordPress crop only the post thumbnails?
- resize images not crop
- Autogenerated Thumbnail compression depending on size
- How to upload imagick resource to media in wordpress
- Upload image from a URL and assign it as a Featured Image to a Custom Post Type?
- Add suffix to filename of uploaded images
- insert post & Upload post thumbnail from the front end using ajax
- Regenerate thumbnails after upload
- Disable wordpress image sizes generation
- WordPress won’t generate image sizes for certain images
- Frontend Post – Allow Only Image File Upload
- Site icons with alpha channel for self-hosted WordPress blog network
- Can I stop wordpress generating media sizes
- Lazyload post thumbnails
- Show featured image next to post-teasers in Genesis Framework?
- WordPress Fancybox Resize Large Image
- How check that there is post thumbnail feature image or not on wordpress?
- If I Regenerate Thumbnails, would WordPress delete the existing Thumbnails and replace them with ‘new copies’?
- Uploading images on front end doesn’t generate thumbnail sizes
- How to get cropped thumbnail source for custom post type
- Can’t seem to attach uploaded image to post and set it as thumbnail
- Update old Post image metadata to ‘thumbnail’ wp_attached_file
- How to stop wordpress always displaying full-res images
- Disable image thumbnails for only one upload folder
- How to replace images?
- Upload featured image from front end using media-upload.php
- “Medium” size image displayed instead of “thumbnail” in only one post, other posts are fine
- How to create resized versions of images added with wp_insert_attachment
- How to fit image to Thumbnail canvas size?
- Process uploads with phpThumb before generating thumbnails
- Redirect to another page using contact form 7? [closed]
- Resize existing library images
- Large image upload size (using timthumb.php
- Filter for post_thumbnail: link to small src and add data-attribute [duplicate]
- WordPress Bug on IIS ? Problem when uploading image on IIS 7
- When does WP resize an image file
- How to resize attachement
- Resize uploaded original images to a minimum automatically
- Else/If Statement to Display Photo Descriptions
- What is the URL pattern for image thumbnails + sizes?
- WordPress Thumbnail compression depends on the server?
- Product Images Low Quality After Updating From WP 3.5 to 4 [closed]
- Cannot upload featured image to a custom post type
- Control resizing of uploaded images
- How to add thumbnails to posts and pages automatically in a uniformed fixed elegant way?
- Removing extra large generated images disables all crops
- SVG not displaying in Media Tab in Backend
- Display Multiple Photos as Featured Image when mouse moves on to it post
- How to use default image as featured image by implement some code in function.php
- unsharp thumbnails after uploading image
- How to delete original image file after upload and resize
- Images uploaded via Gutenberg image block are cropped
- I cannot upload images to post or the media library in wordpress
- Why image Thumbnail url is not displaying with custom size?
- How to disable post-thumbnail from generation?
- Set default “Link CSS Class” in add media admin editor
- Does WordPress have a way of changing the ‘Natural’ size of uploaded images?
- How can i link my featured image to be clicked and the file will be downloaded
- Troubles with code for upload a image
- How to force attachment size for every post
- Is it possible to upload multiple images via Media Library tab in Thickbox I’ve created?
- Making a thumbnail if there exist a link with. jpg or .png extension in WordPress
- Is there a way to force Featured image to show as attachement?
- WP is showing wrong image dimensions
- Generate and upload screenshot as featured image for user-submitted post
- Trying WP editor to load full size image (not ‘300×300’)
- Restricting Image Upload Sizes using ‘wp_handle_upload_prefilter’ – Stuck media progress bar when Featured Image?
- How do I display a PDF thumbnail as a link to the PDF without uploading the image
- Featured Image add tab
- optimized PNGs 5X larger than originals