Some cool image search images:
Hidden Shapes (from an Eagle) in "The Hunting of the Snark"
Image by Bonnetmaker
[top]: Redrawn segment of the print orartie van de Professor L. Wolsogen over syndroom en de nytlegging van de felue gadaen ... by an anonymous artist (1674). The print now is located at British Museum, BM Satires 1047, reg.no. 1868,0808.3286.
[bottom]: Segment of an illustration by Henry Holiday to the chapter The Hunting in Lewis Carroll's The Hunting of the Snark (1876)
Here the pattern matches are not as obvious, as in case of the 2010 comparison (shown in the comment), where the source for the reproduction of Holiday's illustration is a low resolution scan from eBooks@Adelaide. Higher resolution does not always help: Low resolution also is a kind of low pass filtering which you apply to images in order to focus on larger patterns. Therefore I inserted a vectorized low resolition segment (without manual manipulations) of Holiday's illustration into the high resolution scan of an illustration from the 1876 edition of The Hunting of the Snark. (eBooks@Adelaide told me that their scans are from the 1876 edition of the Snark as well. In the 1981 William Kaufman edition of the annotaded Snark you will find slightly different prints. There also are reproductons of Holiday's drawings.)
Why might Henry Holiday have hidden that eagle in one of his illustrations to Lewis Carroll's The Hunting of the Snark? I think that - as in case of most (not all) hidden elements in the other illustrations to the Snark - this is a pictorial allusion to another work or art. This is not about eagles. This example shows that Henry Holiday did not use shapes quoted from other illustrations and paintings in order to enhance the artistic value of his illustration by "stealing" from other artists. Rather, he may have used such copied shapes as "pointers" from his own illustrations to these other works of art. Or he simply used the shapes to construct conundrums. That would be taking references to other works of art, not plagiarism.
