Handy page here on how to ignore files in SVN, a lot of the other comments I see seem to have syntax wrong or incomplete.

http://www.math-linux.com/spip.php?article110

Manual here:

http://svnbook.red-bean.com/en/1.7/svn.advanced.props.special.ignore.html

Note that when a directory is under SVN, the ignore pattern applies to files in that directory only.

I had:
image/upload/100x100
image/upload/200x200 etc

So I had to set the svn:ignore property for each directory separately to ignore user uploaded images (even through I want a copy on the test server from the live server for testing).

I don't know if there is a recursive ignore available, but that is good enough for now.