The simple answer is no, you can't submit a run with just a screenshot. You need a full video of the run from start to finish showing you restart/create the round. Another thing to note is that runs have to be played on a local server by yourself unless you are doing the co-op category. I am not a mod btw so technically it's not a no yet.

Right-click on SCP:SL through steam > Properties > Then type "-scs" in launch options and you should have a create server button next time you get to that host a server screen.