This script in nanDECK takes a sequence (1st line), randomize it (the N flag) and print the 1st element (the 2nd line sets a font and the 3rd print the element):
n[a]=1|2|3|4|5|6
font=arial,128,,#000000
text=1,[a],0,0,100%,100%
Each time the script is validated and build, it gives you a random element from the sequence.
If one need the same, but with images, this is the script (the image files must be in the same folder with the script):
n[a]=orc.png|ogre.png|goblin.png|troll.png|demon.png|dragon.png
image=1,[a],0,0,100%,100%,0,P