All screenshots created by PunkBuster and stored on the game server are in .PNG format. When you download them to your computer it is always best not to open them with any graphics editing software (Photoshop, Paint, etc). If you wanted to attempt to brighten the image for better viewing, always keep the original and use the copy. This will prevent any unintentional alterations being made to the screenshot.
Every screenshot has a unique ID (serial number) which is linked to the game server's PB logs. If these two do not match, the screenshot is considered altered and cannot be submitted as evidence.