That stuff is all dimension thresholds not filesizes.
What I am saying is if your trying to say you upload a photo thats 3 mb in size and your server's PHP max a max upload size of 2mb your file will be dropped by your server even before it reaches the gallery to be processed hense the file is gone if there is nothing to process as in the script goes on
If you get a white screen that is indicitive of another issue.
I really need to know what the exact error is. The picture wont upload is not real descriptive.