Wow, I think I've really found something...

[Midgardsormr]

Not to pooh-pooh Willy's suggestion, but we strongly discourage hosting your images at other sites because it greatly increases the chances that the images will one day vanish. By uploading them here, we're more confident that the information will remain available for years to come.

His suggestion of jpeg compression is spot-on, though. Bmp is an uncompressed format that is actually not very 'net-friendly due to its huge size and incompatibility with very old browsers. Not that I expect to see anyone using Internet Explorer 4.1 these days, but you never know!

Jpeg is good for images with lots of textural detail—satellite style images, for instance. PNG is good for more illustrative images with large swathes of solid colors. Gif is discouraged due to its limitation of only 256 colors, but if you need to show some animation it's an option.

There are some limitations to image sizes that can be uploaded here, though. The file size limit for most files is something like 4.7 MB (higher for some things, like pdf, psd and bmp). I'm not sure about the resolution limit, but it's usually pretty hard to hit that one without first hitting the file size cap.

[WillyWombat]

Not to pooh-pooh Willy's suggestion, but we strongly discourage hosting your images at other sites because it greatly increases the chances that the images will one day vanish. By uploading them here, we're more confident that the information will remain available for years to come.

Oh, good to know!