This seems like a deeper issue to me. I have used this plugin on many sites when changing themes and never had any issues.
As we speak I am using it on a WooCommerce store that we are re-templating. There are over 3,500 images on the site. The previous theme had a lot of custom images sizes and the other developer had changed the sizes of the standard WP images.
I synced down all the sizes for several images before I ran some tests. I compared the results with what I had downloaded. All the image sizes no longer needed are gone and the standard WP sizes are back to normal. Also the images sizes needed for the new theme have been created. The site is on WP 5.4.1
Even though we are working on an offline copy of the website I took a full backup before doing any of this, just in case. Always backup. ??
@sgmax from what you say it seems you used a different plugin first. Is that the case? I’m not sure if you have checked what that plugin may have done to your images but it could have been the one that created the weird image filenames/sizes and messed up the image meta in the database. This plugin can only work with what it sees. If another plugin has broken the images this one can’t fix that.
@dldave what exactly do you mean when you say it had no effect? Did it not create images or not delete ones? It’s hard to make suggestions without specifics.
On a side note @sgmax I understand you’re frustrated but the idiots suggestion was correct. When we start working on an existing website the images are one of the first things we look at. As well as clearing out the junk, one of the best things you can do is use an image optimizer plugin.
I downloaded one of the images from the link you posted above and ran it through TinyPNG (yes it works on JPGs as well ?? ). It reduced the image size by 45%. That’s a big saving especially if there are lots of images on a page. It’s all about page load speed. ??
I have used the Imsanity and “Compress JPEG & PNG images” plugins with success. There are many others, Smush being one of the more popular ones.