The foaf:thumbnail property is a relationship between a full-size foaf:Image and a smaller, representative foaf:Image that has been derrived from it.

It is typical in FOAF to express foaf:img and foaf:depiction relationships in terms of the larger, 'main' (in some sense) image, rather than its thumbnail(s). A foaf:thumbnail might be clipped or otherwise reduced such that it does not depict everything that the full image depicts. Therefore FOAF does not specify that a thumbnail foaf:depicts everything that the image it is derrived from depicts. However, FOAF does expect that anything depicted in the thumbnail will also be depicted in the source image.

A foaf:thumbnail is typically small enough that it can be loaded and viewed quickly before a viewer decides to download the larger version. They are often used in online photo gallery applications.