Absolutely. With a file you just use CFCONTENT, but if your data is anywhere else (memory, database) you can use the response's OutputStream to write it directly. You could even use it to send back a string of HTML if you wanted, but CF provides much nicer ways for doing that (like CFOUTPUT).

Note that in my example, I'm not actually writing to the OutputStream (as Christian's example showed), I'm just wrapping it up and letting the PNGTranscoder write to it for me. I could have used a ByteArrayOutputStream for the PNGTranscoder's destination, and then extracted the byte array and passed it to the response's OutputStream to achieve the same effect, but doing it as I did saves an extra buffering.