Photographic self portrait by Lewis Carroll, and its inclusion into an illustration by Henry Holiday to Lewis Carroll's The Hunting of the Snark. In the drafts and in Holiday's drawing I didn't see that structure.

[top]: Henry Holiday: vectorized segment of an illustration (cut by Joseph Swain) to The Beaver's Lesson in Lewis Carroll's The Hunting of the Snark (1876)
[left]: Original detail
[center]: Low pass filtered detail
[right]: Photographic self portrait by Charles Lutwidge Dodgson (aka Lewis Carroll, May 1875) displayed in mirror view. (Credits for the photo: Watts Gallery, Compton, Guildford)

Perhaps Joseph Swain (the cutter) played a bigger role in this allusion&citation game. I think that C. L. Dodgson (Lewis Carroll) knew about Henry Holiday's allusions. There even may have been a cooperation in combining pictorial and textual allusions. But how can we be sure that Carroll/Dodgson knew about the "hidden Carroll" and the provoking simulacrum (based on a fold in the suit) in that picture?

This comparison also shows, how low pass filtering (blurring) can help. It removes unimportant details in a similar way as our eye/brain "removes" the single dots in a dithered image. In 2009 I initially used the illustrations in the Snark version of Ebooks Adelaide. Due to their low resolution they were blurred renderings of Holiday's illustrations already. Without the blurring I perhaps would not have noticed the first allusion which I found in December 2008.