possibly a simple thing to do but I'm not sure how it's done - I want to remove the permalink from a post thumb, in the default twentyeleven theme. Looked through content.php and the other templates and I can't see where to do this - is this something which should be handled as a custom filter in functions.php?
No idea, never used twenty eleven theme. I opened the theme files. Check out showcase.php around Line 104-118.
Should be on line 115 - just remove the anchor wrapping the post thumb,