PC Graphics
Allways save pictures as .jpg all other file types give file sizes that are too big. The JPEG format does compress the image and reduce it's quality. In programs such as Paint Shop Pro you can set the level of compression and quality. The default setting for .jpg files does not give any noticeable loss in picture quality to the human eye. 
Even pictures from digital cameras and scanners should be saved as JPEG if the default for you digital camera is a .bmp file just load it into PAINT SHOP PRO and "Save As" then choose .jpg file. It also gives you options for the level of compression. Depending on what you want to do with the picture determines how much you compress it. For your own picture archives the default of 15 is OK. However if you have a big picture you want to e.mail changing the compression to a higher number will give you a smaller file size that can be e.mailed easily.
When scanning images it is rare that you would ever need a resolution greater than 300 dpi for scanning photo's etc. Anything above 300 dpi does give clearer pictures however the file sizes will be to big.