Attached Link: http://www.photosig.com/go/journals/read?id=283&forward=userjournalentries

This aroused my curiosity so I went searching the web for the answer. It is the method of taking 2 exposures one with the lens cap on and blending them together to identify the hot pixels from stars. There is an explanation on the link.

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html