I just got my first Captcha here and it only says:
Which is kind of boring, any suggestions for a better one?
In keeping with the blueprint/under construction theme, I'd like to propose this NASA image:
Usage requirement: "Unless otherwise noted in the caption information for an image, the credit line should be "Courtesy NASA/JPL-Caltech."
This could be used generically for all under-construction Stack Exchange sites.
Of course, once the site graduates, it should get its own Web Apps-specific artwork.