Adding a multiple textures using Particular 2.

Hi,

So after watching a tutorial on Video Copilot and playing around with Particular.
It is said in the tutorial that you can use multiple pictures in Particular to create a more random look.
So after searching on the web and trying myself I haven't managed to.

So basically how can you add more than one image to a texture in Particular to create this random look.
I don't want to create a separate particle because that just means a lot more time being spent.
Plus I don't think the look will be as good.

Please let me know if this is possible and if so how.
Many thanks.

Ali :)