3) realize that even in the absence of <input type="img"…>, if you are doing things like:
"...the HTML input element had a background image specified and a text-indent:-9000px property applied to it, which puts the standard text for the button way off the screen, leaving only the background image visible."
then you're doing it wrong. What the hell?
Also regarding the PNG/JPEG rule of thumb, it should be: JPEG for photographic images, PNG or GIF for everything else on the web. Large doesn't and shouldn't necessitate JPEG. Then you end up with ugly, artifacted, JPEG screenshots, and these already exist aplenty.
I think you failed to recognized what's wrong with the section I quoted. Negative text indent is fine. Negative text indent for the purposes of "[putting] the standard text for the button way off the screen, leaving only the background image visible," is a ridiculous misuse of that CSS property.
"...the HTML input element had a background image specified and a text-indent:-9000px property applied to it, which puts the standard text for the button way off the screen, leaving only the background image visible."
then you're doing it wrong. What the hell?
Also regarding the PNG/JPEG rule of thumb, it should be: JPEG for photographic images, PNG or GIF for everything else on the web. Large doesn't and shouldn't necessitate JPEG. Then you end up with ugly, artifacted, JPEG screenshots, and these already exist aplenty.