Hi,
You can use HTML or markdown of uploaded image in the option field (or in the composer):
For example:
[poll type=regular results=always public=true chartType=bar]
* option 1 <img src="upload://tpbXHFLPCTLWjyGvtyekmXQN49A.jpeg">
* option 2 
[/poll]
Will result to this poll:
- option 1
- option 2
0
voters