The Documenta Image Format
with square thumbnails, 150px, On-click: permalink, counter: 4

Through the Exhibit Options Button or the Refine Button in Preview, you can change
*the thumbnail size & shape
*number of columns (Counter)
*On-Click image display (Overlay or Permalinks: a slideshow)
*location of text like this to either the beginning or end (location of files)

Seems to work better without captions, because the captions show up under the thumbnails, making a confusing visual.

You can change the
overlay background color (for On-click: overlay)

If you want captions in the full image but not the thumbnail:
1. Find this file: format.documenta.php
2. Add the following two lines after line 237:
.media_title { display: none; }
.media_caption { display: none; }