Clickable image poll: Precisely define graph extent and "0" position.
The current reporting on Clickable Image is in terms of "% of full extent of the total uploaded image". This method would work well for capturing quantitative data based on a graph (an image of a graph),

but only if <
three points on the graph image could be precisely defined (in terms of screen position) by the user: (0,0), (0,100%), and (100%,0). Then, the reported percentages would mean something more directly usable.
Suggestion: Offer this capability from the "Edit" screen that shows the uploaded image at the largest scale. From there, the poll creator would click on 3 different places on the image to show where the 3 points are. Then, the creator could upload and use any existing x-y graph - complete with axis labels and numbers, colors, etc.
The attached file shows the kind of existing grid image I would like to use. In this case, the (0,0) position lies toward the lower left - but it is NOT at the extreme lower left of the image because there are axis labels and numbers. Similarly for the two 100% positions. You could also allow the poll creator to redefine the actual values; e.g. "100% = 5.0" in this case; but that's a minor detail.