underscore978 on "link to search results from image page"

i am trying to create a theme and i would like your help with the syntax of a link.
when i do an image search, results come up in the search page and from there you can click any image thumb and take you to the image page.
I would like to have a custom link on the image page that can take you back to the search results page where the image came from but im not very familiar with php syntax so pls help ...
thank you