This may help DCS users get the best out of their screenshots:
Edit the "options.lua" file in something like Notepad++ or Wordpad (Windows Notepad makes a hash of it). It should be in something like: C:\Users\[username]\Saved Games\DCS.openbeta\Config
1) Make a backup!
2) Find the ["graphics"] section.
3) Check that the dimensions are what you want:
["height"] = 1200,
["width"] = 1920,
4) Set the filetype and quality values:
["ScreenshotQuality"] = 100,
["ScreenshotExt"] = "bmp",
The format may be jpg, bmp or png. The quality value (higher=better) only really applies to jpg files, though technically it also applies to png files, as it can affect filesize/time to decompress (it's still lossless though).
Images are stored in something like: C:\Users\[username]\Saved Games\DCS.openbeta\ScreenShots and are triggered by the PrtScrn key by default. Don't forget to turn off the labels (SHF F2) and info bar (CTL Y).
For screencomps, make sure your width is at least 1280 (don't forget to check the aspect ratio/height if you set it to a non-standard width). Preview images in the screencomp thread can be jpg or png, but remember to keep an uncompressed/uncropped version in case it's needed for a banner: png or bmp.