Indy a quick tip. This is to further your knowledge. You wont be able to print these logos submitted in this contest on t-shirts. Only vector images can be which are huge files. Most of these images are google.com/images searches.
Well not only vectors can be printed to t-shirts, although it is true that these are all too small more than likely. You can print most design work to shirts as long as they are in a high enough resolution. Depending on the type of printing used, you might require vector files though.
Davey boy is right but most of the pictures on this contest look like google images. And those cant be printed well.