When using the image picker in a front end form when installed in Jooma, I am still getting the "You are not authorised to view this resource." message so am unable to use it.

The problem with the image picker come from Joomla. There is an opened ticket on this. You have to apply a patch.

Here the ticket :
joomlacode.org/gf/project/joomla/tracker...racker_item_id=25288