I you haven't alreay create an album in the gallery. Upload the picture. Go to the album and find the pic, right click the pic and copy the address. Go the contest album and click on the picture icon and paste the address. Or at least that is how I do.
An easier way is to create an account at photobucket.com, upload the pic. Save it and click the IMG code right click on the highlighted code. Go the contest album paste the code.
Now you are totally confused. . .