This issue I think discussed a lot here, try to submit an item with .gif image and see if it display normal on the homepage, if it is displayed then your gif2png executable file is working fine.
I don't know if it is just a coincidence or not but when I try to upload a picture with a long file name like ( B.J. Surhoff - opps 1990 - Card #696 ) I get a box with a red x but if i delete that file on the listing page and shorten the file name to ( B.J. Surhoff -2 ) it will upload fine. I now get a picture instead of a box with a red x....
In my case at least the red x is caused by the file name on my hard drive being to long. Once I shorten it the picture uploads OK...
NO NO, it looks like I was wrong about the length of the title causing the file to upload as a red X.....
It was the Pound sign (#) doing it to my uploads. If I had the Pound sign in the title of my sports card it would not upload the file properly and I believe it may be because I have my system set to Safe HTML rather than All HTML