User blog comment:Trellar/Screenshots: Tips & Tricks/@comment-227438-20120329202101/@comment-957747-20120330021927

JPEGs are not good to use for images that are viewed often. Like Fritz explained, the lossy format of JPEGs cause it to lose quality each time the image is viewed. This means that routine virus scanners can actually lower the quality of your images over time. GIF and PNG are much better (TIFF too) to save images so that they are the same quality as they were when you saved them.