The datatype of some properties is apparently "imgResource". Taking a look at the definition of the datatype, we learn that it can do one of two things.

Either "imgResource" is a file-reference after the same concept of "resource" but with a few additional properties to modify the image.

Or "imgResource" is a GIFBUILDER-object, which lets us design an image by combining graphical objects like other images, text and solid filled boxes.