You should typically convert your JPEGs to a lossless format as the first step before you edit or crop the pictures. JPEG (also spelled JPG) is a way to reduce the file size of mages, and it's ideal for creating photos you can easily put on Web pages or send as attachments in e-mail. But JPEG compression removes parts of the image. When you work on a JPEG photo and then save it, you make the problem worse.

As soon as you get the pictures out of the camera, save them in a lossless format and work ONLY on the lossless versions. (Save the original JPEGs in case somethng goes wrong.) A good choice of a lossless format on Windows is BMP or PNG; on Macs or Linux, it's TIFF or PNG. Windows users can also use TIFF, and Mac users can …. or, well, you get the point.