I look at a couple of methods of creating a passport stamp effect in Photoshop CS3 and settle on the “Noisy Cloud Filter” method.
There are a few different methods that can be used to create a rubbers stamp affect in Photoshop, including the use of the spatter filter (Filter -> Brush Stroke -> Spatter), as describe in in the Draw a photoshop rubber stamp effect article on oogletutorials.com, or the use of the cloud filter (Filter -> Render -> Clouds) with some noise added (Filter -> Noise -> Add Noise), as describe in the Passport Stamp article on thedesignworld.com.
For the Lavykim Australia stamp example I used the Noisy Cloud Filter method, and was reasonably happy with it. However, rather than creating the text and then wrapping it around a semi circle using the Wrap Text option and then duplicating and rotating the wrapped text, I used the path tool to draw a circle, as described on the Adobe site. This method involves creating cirle path and then positionion the type tool over the circle at the point where the type is to begin. Once all type has been entered the character palette (Ctrl+T) is used to ajust text size and spacing, such that the text wraps around the circle completely. The advantage of this approach is that, it is possible to have different text on both sides of the semi-circles.