Updated 2/6/2012 after ISM’s merger, which seems to have dramatically changed their pay structure.
Updated 7/1/2011 with information about ISM’s “Photostitial Units”, ads that appear automatically and hide the first image a user sees.
Image Space Media has an interesting idea: overlay images with advertisements that appear only when users hover their cursor over the image. Try it out by hovering your cursor over the larger images on this site. They’re currently calling it beta, so there’s every opportunity they’ll improve over time.
It already seems to work well, though. Hover your cursor over an image (such as my picture of the New York City Skyline at night), and an advertisement rises up from the bottom, covering about one-quarter of the image, as shown here (scaled down to fit this page).
There’s also a sharing icon in the upper-left corner that you can turn off. If the user clicks it, a full-page overlay appears that provides links to sharing on Facebook , Twitter, and e-mail. Several ads appear on the page, too, and it shows you popular and recent images. This picture shows a scaled-down version of the sharing page, however, since I’m currently using ISM on this site, you can experience it for yourself by hovering your cursor over it.
Once you’re hovering, you can click the advertisement or just move your mouse away. Once you move your mouse, the advertisement shrinks back down to one line. You have to reload the page if you want the ad to completely disappear.
It’s smart enough to ignore small images, such as those you might use in menus. Occasionally, the advertisement wasn’t flush with the bottom of the image, but I’m sure they’ll work that problem at.