Yes, press F9 for a screenshot.
it will be stored in your system directory.
But indeed, the problem is that they are too dark.
Put some more contrast/brightness in them with photoshop or paintshop pro or another image editing program.
if you wanna create a little 'movie' then you can make a demo.
bring up the console and type demorec name. like 'demorec mymovie'. and it starts recording. if you want the demo to stop recording, bring up the console and type 'stopdemo'.
if you wanna view it, bring up the console and type 'demoplay mymovie' or the name you gave it. enjoy! nice way to tape a clanwar so you can discuss it later or to prove an aimbotter. there is a nice UT Demo Manager. try to get it somewhere, I can't find the url now...