.eps images referenced by asciidoc .txt source files show up beautifully in the pdf docs, but don't show up at all in the html.
For example, look at the Integrator's manual, section 2.1 Servo Systems/Basic Operation. That section starts with a paragraph of text, then it says "images/servo-feedback.eps" and "Figure 1. Servo Loop", but the text "images/servo-feedback.eps" should have been replaced with the named image. Then there's more text, and below that there's a .png image which shows up well in both pdf and html.
Back in 2.4, before asciidoc, we converted .eps to .png before including them in html, using commands like this:
convert -density 96 -resize 1000x9999 parport-block-diag.eps parport-block-diag.png
identify -format '%w %h' parport-block-diag.png