Click on this support page as a good starting point for understanding Custom Test Types.

Custom test results comprise one or more files, typically documents or images, or media files.  A test result comes with a thumbnail.  These thumbnails are used in the ‘gallery’.

If the test only contains one single file, the thumbnail is automatically created by Audiqueen.  But you can overwrite it with a thumbnail of your choice.  For this, you need to upload the thumbnail (see scenario B below).

If the test contains multiple files, you need to set the thumbnail manually.  You can do this by dragging and dropping one file to the thumbnail frame (A) or by uploading an image from a location on your PC (B).

This feature is not available in the web viewer.  
Audiqueen's web viewer displays the results entered in Audiqueen's Workstations.