Once you have built the election and corresponding ballots, you will need to upload all the bio pictures to the "Gallery" section inside of any organization page. Then click on your image, right click on the image, and click Copy Image Address.
Once you have copied the image address, click on the ballot question again and click the "Edit" icon . Go to the "Answers" tab within the question and click on the answer choice in which you would like to add the image to.
Click on the "Include Additional Text" checkbox and you should see a Tree icon in the toolbar of this textbox. You will be able to paste the download link that you copied into this Image URL field. You will now be able to resize the image as well.