The scripts make three thumbnails from the original (named <userid>_<filename>). I'm getting fatal errors during the creation of these after the first one is generated. One thumbnail is a custom size called <size>_<userid>_<filename> (size depends on the settings for the contest) the other two are called med_<userid>_<filename) and pre_<userid>_<filename>. You can ftp into the .../wp-content/plugins/wp-photocontest/contests_holder/<contest name> folder to see them.
I'm running out of memory with 30MB allocated to php and hoping to raise this to 60MB. For me the break point is somewhere between 330kb and 430kb for original image file sizes.
So when the script hits the fatal error (and dies) during this process it wont get to the database updating but will leave files on the server that prevent re-uploading because there is a file-exists check based on the original filename.
One possibility is to add a file_size check to the code to kick out any upload above xKB before it tries to generate thumbnails but this is site specific. I'd rather get more memory. I suggest you call the tech support guys at the hosting company you use to get the real memory limits you have and explore options with them. PHP scripts only set and return settings that for me are completely fallacious being over-ridden by hosting account settings. I don't know what happens with really large image files and more memory yet. So even then a file size limitation may still be needed given today's digital cameras with as much as 18MB sensors.
May be frekel will have other suggestions (and corrections to my analysis).
Hope this helps.