I have a headline and an image - can I test both elements and then put multiple conversion codes on the thank you page?

It's all done on cookies - when a prospect views a page with a Split Test A/B Dynamic test on it, a cookie is placed on his computer.  Then when he arrives at the "destination" the relevant cookie is read and the relevant count incremented.  For 2 tests on the same page, 2 cookies will be placed and both will be incremented on accessing the "destination" page and so invalidate the tests ...  The best solution is to test one element at a time! Once you find a "winner" for one test, move on to test the winner as static and changing something else.