You can take a screen shot in-game by hitting the PrtScn ("Print Screen") button on your keyboard. A compressed JPEG image file will be created. If you press Alt + PrtScn an uncompressed TARGA (.TGA) image file will be created. In either event, the screen shot images are stored in the {Local path to program}\Cryptic Studios\Star Trek Online\Live\screenshots\ directory. The image saved does not include the User Interface, however.
To take a screen shot with the User Interface, use the command /screenshot_ui (for TGA) or /screenshot_ui_jpg (for JPG) in the chat box. You may also bind a key to this — /bind P screenshot_ui, for example, will bind the P key to the /screenshot_ui command.
The option /renderscale # will scale to some multiple # of your monitor's screen resolution (/renderscale 1 is default). Thus, /renderscale 2 will be an image 4 times as larger as it doubles the width and height. Running renderscales much higher than 2 or 3 can result in crashing the game. Resizing these later to your screen resolution can provide a type of antialiasing.