Team Fortress 2 (PC) (external link) allows you to take screenshots in game without requiring third party software. Firstly you will need to ensure that a screenshot button has been configured in game, this is setup under the Options menu and is located at the bottom of the scrolling list:
As you can see in the screenshot I have configured my screenshot key as F5, once in game pressing F5 will create a TGA screenshot.
To find the the created screenshots you can have to navigate to the following folder where <steam id> is your login id, if one of the folders does not exist then try the other one:
- C:Program FilesSteamsteamapps<steam id>team fortress 2tfscreenshots
- C:Program FilesValveSteamsteamapps<steam id>team fortress 2tfscreenshots
TGA files are not very common and as such you generally won’t be able to view them without additional software such as Quicktime. In order to convert them into more manageable files such as JPG or BMP I use the open source image program GIMP, it’s a bit overpowerful for this task but is very easy to use. If you have trouble with it you could try IrfanView instead which is more user friendly.