tomf1990 said:
i would not recommend using jpegs as they loose quality over time. They are also falt images which do not support layers, i would use either RAW, TIFF or PNG but i do not think that paint exports to these.
Jpg files can be quite adequate, depending on their use but you do have to be aware of some aspect of the file format. It is lossy compression. The higher the compression the smaller the file size and the lower the quality. I oven use 20% compression and get adequate quality for website images.
If you continue to save the file it will get worse, so you are best to leave the original master and save to a new file.