Visual confirmation breaks the page layout in prosilver's mobile mode on registration page.
See the screenshot.
CAPTCHA image is surrounded with padding of total 60px. The smallest screen is 320px in width. So maybe generating CAPTCHAs of 260px in width would solve this problem?
Marking as block for 3.1.0 since the patch is already there just needs a bit more work.
Second patch with a minor change: