You can set up number of selections the respondent will be able to make on the image you have displayed. The maximum number of selections are 20.
You can select a color for the border of the respondents selection.
The Highlight Clicks option allows you to collect the exact coordinates of respondent clicks on an image. You can enable this option from Heatmap question settings: You can also limit the number of points a respondent can select / click. If a respondent exceeds this limit, the latest selection will replace the oldest one.
Once this option is enabled, respondents see a small dot where they click.