Pinki 1.1.1

Pinki is a menu bar item that creates permanent Mac OS X icon thumbnails for image files based on their image content. For example, if you download the images "34-234.jpg", "563-641.jpg", and "moose.png" using your web browser, and the file icons are generic "JPEG" and "PNG" icons, you have three choices if you wish them to have custom thumbnail icons:

One at a time, open each image in Preview, use the 'File->Copy' menu, close the image, Get Info on the file in the Finder, highlight its icon in the info box, and use the 'File->Paste' menu.
Navigate in a Finder window to the folder where the image file is located, select the 'View -> View Options' menu, then click the box labled 'Show Icon Preview'. (The downfall to this is that each time you open the folder your computer will have to re-read the files and assign custom icons to them, which can take a lot of processor power and memory and can slow even new machines down quite a bit. In addition, when you use the "Show Icon Preview" option, the custom thumbnail icon data isn't actually saved inside of the image file itself - if you were to move the file to a different folder or copy it to a different computer the custom thumbnail will disappear.
Simply select (highlight) the three files all at once in the Finder, and select "Create Thumbnail(s)" from the Pinki menu item. Or to make it even simpler, just hit Command-Shift-T on your keyboard after selecting the files.

Pinki can also remove custom thumbnails (restoring icons to their generic state) as well as save thumbnails as separate .icns files. Pinki supports all major image formats including jpeg, png, tiff, gif, psd, pdf and bmp.