The Yale Image Finder searches PubMed Central articles for images.
That sounded not only like a good idea, but a good idea I’d heard before. In July of 2007, I posted about UC Berkeley’s BioText
The answer is found in this Bioinformatics article
The authors note they are aware of BioText, but that…
…we are not aware of a biomedical search engine that can retrieve images by searching the text within biomedical images. This offers several advantages over searching over captions alone. First, captions may not contain all the textual information that is contained in the images. Second, image texts are usually very speciﬁc, allowing for precise matching of images with related images.
Neat. So Yale’s tool does OCR on text appearing in images and adds that text to its searching index of images in PubMed Central. Cool.