Mac OS X devotes a huge amount of disk space to custom icons and previews. It can be as much as 120K per file. This overhead is substantial for for small .jpg files.
This is a big problem if you are storing thousands of .jpg files or if you are just trying to email a .jpg file to someone. Mail.app has a bug in it that makes it send the icon and preview as well as the file. If you're using Mail.app, it's a good idea to delete the resources of .jpg files before sending the file to someone else.
The easiest way to delete icons, previews, and other file resources from a bunch of .jpg files is to install Grim Ripper. Select some files, Control Click and choose Delete Resource Fork.
So you don't believe these numbers? Try this: View Mac OS X Hints with Internet Explorer. Look at the logo at the top of the page. Click and drag the Mac OS X Hints logo to the desktop. The file name should be logo393ss1.jpg. Select the file and pull down File -> Show Info. The file takes up 132 KB. But the real file size is only 12 KB! To see the real file size, open up Terminal.app. Once there type these commands (sorry they're scary Unix commands, but stay with me):
% cd desktopNote that the 'cp' command is the normal Unix copy command. It copies the file only, not the Mac OS X icons and other resources. Select the new file on the desktop, logo.jpg. Pull down File -> Show Info. The file size is only 12 KB! Double click the file and it shows up in Preview just fine. That means that the preview and icons take up 120 KB for a 12 KB file!
% cp logo393ss1.jpg logo.jpg
% exit
Mac OS X Hints
http://hints.macworld.com/article.php?story=20021030070114812