What kind of image is it?

There are a number of ways to decrease filesize. These include lowering quality if it's a JPEG, lowering the number of colors if it's a GIF or PNG, or (if it's a very small PNG) converting it to 24bit PNG.

(the last one sounds astounding but it's true. My theory is that the indexng of colors takes up more room than the 'lol use any color' information. This usually happens in the 1-1500 byte range)

Post the image here and one of us can perform the necessary voodoo rituals to get your proper size.