I checked for posts with a similar problem, but couldn't find a solution.
I've uploaded an example of my problem here:
I'm using the latest Gravity Forms [version 1.6.11] with the picatcha add-on [version 1.1] (it should be displaying below the 'So I know you're human' part is).
The picatcha images do display correctly in the form editor.
I'm using Wordpress 3.5 with Headway 3.4.3 (I'm putting the shortcode in a 'custom code' block, for anyone familiar with Headway). The shortcode I'm using to embed the form is:
[gravityform id=2 title=true description=false].
This is my first form using Gravity Forms, so any help would be much appreciated!