Changing PIC1.PNG for homebrew...

So I just installed SCUMMVM homebrew for PS3. The background was awful, so I made a better one, but when I replaced it nothing shows up. The file is named correctly, all caps, and is actually smaller in file size. Is there another step involved? Is there any tools that can recompile the pkg or anything to that extent, or is there and easier way?

I may be using SCUMMVM as an example, but I may do this for my other homebrew as well, so the easiest method is greatly appreciated.