As a WordPress site owner, one of the most frustrating errors you can encounter is the "post-processing of image failed" message when trying to upload an image.
This common image upload error can completely block you from adding images to your pages and posts.
According to surveys, around 22% of WordPress users have encountered this error at least once.
The good news? With some targeted troubleshooting, you can eliminate this error and significantly improve your site‘s performance at the same time.
In this detailed guide, I‘ll draw upon 15+ years of experience managing WordPress installs to walk you through exactly how to troubleshoot and fix the post-processing failed error for good.
Contents
What Happens During Image Post-Processing in WordPress?
Before we fix the issue, it helps to understand exactly what post-processing means.
When you upload an image in WordPress, several key things occur:
-
The raw image file gets uploaded to your WordPress server.
-
WordPress generates multiple smaller resized copies of that original image. For example:
- Thumbnail (150x150px)
- Medium (300x300px)
- Large (1024x1024px)
-
WordPress extracts all the image metadata like EXIF data, orientation, size, etc.
-
The image data gets optimized and inserted in the media library.
-
An attachment post is created containing the image properties, captions, alt text etc.
This resizing, data extraction and optimization is called image post-processing.
By default, WordPress relies on two PHP image libraries to handle processing – GD Library and ImageMagick.
The post-processing failed error occurs when an issue with one of these libraries prevents the image from being fully processed.
Common Causes of Post-Processing Failure
Here are some of the most common reasons why image post-processing fails in WordPress:
1. Large Image Sizes
Uploading high-resolution images that are very large in file size can overwhelm your server resources and cause post-processing to crash.
For example, a massive 6000 x 4000 pixel image from your DSLR camera may work fine on your computer but fail during WordPress processing.
Recommended maximum image sizes:
| Image Type | Maximum Size |
|---|---|
| Raster Images (JPG, PNG, GIF) | 2500 pixels (width or height) |
| Vector Images (SVG) | 5000 pixels (width or height) |
2. Low PHP Memory Limit
Post-processing requires a certain amount of server memory resources. The default PHP memory limit allocated to WordPress is typically 40-128MB depending on your host.
This low memory can crash when attempting to handle large, high-resolution images with many colors, shadows, gradients etc.
3. Server Load and Timeout Issues
If your WordPress host has too many sites on a single server, during traffic spikes, the server CPU and memory may be completely maxed out.
This lack of available resources leads to post-processing timeouts and failures.
Similarly, low PHP timeouts can cut off processing of images prematurely. Default timeout is 30 seconds, which is often too low.
4. Problems with ImageMagick Configuration
While GD Library works fine in most cases, ImageMagick tends to be more prone to issues because it requires additional dependencies and configurations.
For example, a missing or incompatible ImageMagick extension or library can prevent image processing from completing properly.
How to Troubleshoot and Fix Post-Processing Failed Errors
Now that you know what causes these errors, let‘s go through some troubleshooting and solutions:
1. Check for Temporary HTTP Errors
The first step is to rule out a temporary glitch. Re-upload your image after some time and see if it works.
You can also try:
- Clearing your browser cache before re-uploading.
- Using a different web browser or device to upload.
- Renaming the image if the filename has special characters.
This takes care of any intermittent hiccups. But if it occurs consistently, move on to the next recommendations.
2. Increase PHP Memory Limits
Based on my experience managing WordPress for clients, low memory is the culprit behind post-processing failures in most cases.
You can easily increase PHP memory by adding this line to wp-config.php:
define(‘WP_MEMORY_LIMIT‘, ‘256M‘); The higher the memory, the more image processing resources are available to WordPress.
Recommended PHP memory limit based on traffic:
| Site Traffic | Minimum Memory Limit |
|---|---|
| Less than 50k visitors per month | 64 MB |
| 50k to 200k visitors per month | 128 MB |
| 200k to 500k visitors per month | 256 MB |
| 500k to 1 million visitors per month | 512 MB |
| Over 1 million visitors per month | 1024 MB |
If you‘re unable to edit wp-config.php directly, use a plugin like WP Native PHP to add this code snippet.
3. Optimize and Resize Images
Heed the error message‘s advice and try uploading a smaller version of the image.
Use an image optimizer like Smush or ShortPixel to:
- Compress the image and reduce the file size.
- Resize to a smaller, web-friendly size.
- Convert to a supported format like JPG or PNG.
Here are recommended image sizes for web:
| Image Use Case | Maximum Width/Height |
|---|---|
| Header / Hero Image | 2000 pixels |
| Blog Featured Image | 1000 pixels |
| Article Body Images | 800 pixels |
| Image Thumbnails | 400 pixels |
Properly resizing and optimizing your images not only fixes upload errors but also improves page load speed and web performance.
4. Switch to GD Library for Image Processing
While both GD and ImageMagick are installed in WordPress by default, I recommend switching the default image processor to GD Library.
In my experience across various WordPress projects, ImageMagick is more prone to configuration issues and failures. GD Library has better performance for the common image editing needs of a WordPress site.
You can easily switch the default processor to GD Library by adding this code:
function wpb_image_editor_default_to_gd( $editors ) {
$gd_editor = ‘WP_Image_Editor_GD‘;
$editors = array_diff( $editors, array( $gd_editor ) );
array_unshift( $editors, $gd_editor );
return $editors;
}
add_filter( ‘wp_image_editors‘, ‘wpb_image_editor_default_to_gd‘ );I recommend using a plugin like WPCode to add this snippet without modifying core files.
This prevents conflicts with ImageMagick and resolves most post-processing errors.
5. Review Server Configuration
If you have access, also review your PHP and WordPress configuration for optimal image handling:
- Increase timeout – Default 30 second timeout may be too low for large images. Raise it to 60 or 120 seconds.
- Enable background processing – Take advantage of cron and WP-Cron to process images in the background.
- Add caching – Caching layers like LiteSpeed Cache or W3 Total Cache prevent timeout during processing.
Proper WordPress server configuration tailored for your specific site traffic is crucial.
6. Upgrade to Managed WordPress Hosting
If you are on a basic shared host with limited configuration access, I recommend upgrading to managed WordPress hosting like WPEngine or Kinsta.
Managed hosts offer:
- Optimized web servers and resources to handle image processing.
- Ability to raise PHP memory limits.
- Integrated caching and CDNs for faster image handling.
- Automatic image optimization.
For resource-intensive sites, managed WordPress hosting is the best solution.
Prevent Post-Processing Errors Proactively
Here are some tips to avoid these image upload errors before they happen:
- Actively resize and compress images using ShortPixel or other tools before uploading.
- Limit upload size to a reasonable maximum like 8MB.
- Manually review large images before uploading.
- Use front-end image optimization plugins like EWWW.
- Switch to alternative processing libraries like Imagick if available.
Proactively optimizing your images will eliminate most processing errors and speed up your site too!
I hope this detailed guide helps you troubleshoot and fix the pesky "post-processing failed" error in WordPress for good. Let me know if you have any other questions!
