Ok i got it to work I think but its a bit of a hack, i thought something like this would have been a basic feature with quip.
Because quip doesn't have the ability to create extended fields i have used the website (as I'm not using it) field to store the location of users image in the quip db table.
So when the users posts it passes the hidden value:
<input type="hidden" name="website" id="quip-comment-website-[[+idprefix]]" value="[[+modx.user.id:userinfo=`photo`]]" />
And to display the photo in the quip comment I can just use the supplied website placeholder with phpthumb to resize it
<img src="[[+website:phpthumbof=`w=50&h=50&zc=1`]]" class="quip-avatar" alt="" />
This works which is great, although it doesn't seem the best to be using the website field to store the data....
....the only problem now though is if the user changes their photo. This will not be reflected in older comments, generally on a website or forum your image would change across the whole site to the current image....any thoughts?