You are really unclear in what you want, so I am going to have to do a lot of guessing... Here is what I think you are doing:
You have a NSTextView (Rich Text Enabled) that you want to syntax-hilight. You have gotten the NSMutableAttributedString from the appropriate NSTextStorage object and you would like to find the NSRange of an <img> tag. Do I have things so far?
If so, then you are barking up the wrong tree to try and do this with regular expressions (a wild-card is a regexp concept). You need to create a state machine, or use one of the many html state machines out there.
If you really feel that regexp is the way you need to go, then take a look at OmniGroup's OFRegularExpression in
OmniFoundation.