I recently needed to have thumbnails for some images that we uploaded to SharePoint for display in a thumbnail library.  I couldn’t find any documentation on how to get a thumbnail for an image.  So I fired up Fiddler opened up the script and figured out what the hundreds of lines of JavaScript was doing behind the scenes.

Basically, you take an append _t to the directory, convert the period in the file name to an underscore and append .JPG.  Here are a few examples:

Using a _w instead of a _t seems to give a slightly larger image.  This might be useful for hover over events.