There are a few ways to take a screenshot ingame.

But the 2 most common ways are using the inbuilt wolfenstein camera or using xfire.

First for wolfensteins camera,

1) Bring down the console using the ~ tilde key (located above TAB) and type /screenshotJPEG (then the name of the screenshot here) this will take a screenshot of anything on the page at the time in JPEG format. Then, to find this screenshot goto your wolfenstein folder > etpub > screenshots.

2) Using xfire: Run xfire before you go ingame, then when you want to take a screensot using xfire, simply hit the keys: Scroll lock + s or whatever keys you have prechosen in your settings.