UPDATE: November 17th, 2019
Nothing is worse than a website error. Worse and annoying.. Today, while I tried to manage a website of a client, I found a WordPress 5.3 Upload error. “Ok”, said to myself, “let’s found the problem and fix it.” . First thing I did was to look at the image properties, to see what is the real size of it. The size of the image were about 1900x320 ( far lower than the recommendation from the inside of the error ).
Hmm… Strange. Usually I don’t have this kind of problem, even if I upload big-size images ( which is very rare, but anyway ). So, like any other man, I start to research about this issue.
First thing I did was to take a look on WordPress Support forum. The users from there usually found quickly these kind of errors and also come with solutions. But this time I was unlucky. Well, next step was to search on Reddit and I found a temporary solution for this problem, until WordPress will solve the issue:
Post-processing of the image failed. If this is a photo or a large image, please scale it down to 2500 pixels and upload it again.
To temporary solve it, you have two options:
1. Add this line to the functions.php of your theme ( or of your child theme ):
add_filter( ‘big_image_size_threshold’, ‘__return_false’ );
Pay attention to the actions you make, because you can broke the entire website.
2. ( Safer ) Install the “Disable “BIG Image” Threshold” plugin, provided by Jonathan Desrosiers ( Many thanks to you, Jonathan ). You can search the plugin in your Admin Dashboard area -> Plugins, or download it from here: https://wordpress.org/plugins/disable-big-image-threshold/