The key to putting up images on the web is optimisation. It's vital to compress the images down as much as possible as large images = unhappy surfers.
60% enjoy high speed web access but there is still a lot using with creaking dialup modems - and don't forget those on the road accessing through laptops and slow data cell phone connections of PDA's
People don't like to wait for pages to download, so if we work on the assumption that they'll start to get twitchy after a nine second wait, that gives you an upper limit of an 18k page size for 14.4 modems, 35k for 28.8 or 85k for 56. Not much to work with!
Keeping the load time of your pages down is critical. The larger the file, the longer the user is has to wait for it to appear - and the more likely they are to leave and go elsewhere.
Most digital cameras come with graphics programs which offer tools to optimise and export files in the most popular web formats.
Software for Optimising Pictures for Websites