This is a base template for a single-choice poll with images:
[poll name=poll1 type=regular results=always public=true chartType=bar]
# **Poll Question**
* Paste/Upload image here <br> [Text](Link)
* Paste/Upload image here <br> [Text](Link)
* Paste/Upload image here <br> [Text](Link)
[/poll]
Basically, paste/upload your image into your reply window and put it in the right place, add some option text in the [Text] brackets, and a link in the (Link) ones.
A good size for poll images is 150x200, or 125x166, depending on how many options you have.
And the full instructions are in Bonus Formatting - #41 by Ian_Chimp 