This works for the Crowdsource Image URL HITs on mTurk for google only!
(link: https://www.mturk.com/mturk/preview?groupId=35DGDVUOGJ2PY1BH3OWZQI24VQ9YPD)

Change log:

2014-06-26
- Added minimal parsing to correctly return either the page or direct image URL as requested in the instructions.

2014-05-02
- Modified image search to use google.co.uk since postMessage seems to bug out only on google.com. I don't think this should affect the HIT.