I used a 3rdparty image merging watermarking script to watermark some images, though it did the job as it should the result was the kind of disastrous the folder/dir size went from 3GB to 9GB.
So I was thinking that regular watermarking would be a better option rather then image overlaying, but I can’t seem to find anything about wm backgrounds only text, what I want is a white section overlay at the bottom of each image and text inside that section, basically like 9gag.com but on top of image rather then below.
example:

The problem is likely the output settings. Watermarking itself should not add to the process, however when generating a “new” image, there’s a good chance the optimization/compression settings weren’t the same as the original image (setting it as anything lower than the original image won’t gain any quality since the information is already lost, so keep it the same or set it higher).