Create competitions and share them with your friends. Anyone with the link can take part by voting on the winner, even if they don't submit pictures.
You and your friends can submit one photo each. Photo Clash doesn't host your photos. Instead you just enter a public link to the image on Flickr, Facebook or where ever it's already online.
Remember, you can't vote for your own submission. After the competition ends you'll be able to see who's won. Photo Clash also gives you your own page, showing you all your entries, how many votes they received and which ones won.