injunjoel has the best advice so far: move your image generation into a seperate CGI, and refrence the URL of that CGI in your IMG SRC tag.

If, for some reason, you really *MUST* have only one script, then you a super search for "inline images" suggests these node:

• nearly identicle question
  • suggestion to use URI::Data (which reportedly doesn't work on many browsers)
  • a working example of data URIs
• suggestion to use mime/related and refrence the images by cid.
  • an example of this in email (doing this in a CGI instead of an email (or finding a node that allready does) is left as an excercise for the reader.