It really doesn't make sense, sometimes the way the image was originally compressed can cause this type of problem.
Does that mean you're changing the encoding of images
by default? I'd say you shouldn't do anything to the image, unless the user requests for a compression change.
In theory there is always a "create ", especially because the system eliminates all metadata from the images. To do this he has to "create" a new image. What shouldn't happen was increasing the size of the image. There may be some byte differences but nothing significant.
That's why I find this case strange.