My photo site (I roll my own and use Gallery) resizes photos on the fly. What I did was to first select the large photo and copy it's location (the same you would do if inserting an inline image) and put that as a URL, then I got the smaller photos location and wrapped it in IMG tags (how you insert inline images), finally I closed the URL tag (by /url). Here is an example:

Code:
[url=http://LARGEIMAGEADDERSS][img]http://SMALLIMAGEADDRESS[/img][/url]


That makes a clickable hyperlink with an images as it's "friendly name".

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