Thanks for getting back to me Steven.
I don't like fit to fill . The images I was using in my website looked very amateurish as thumbnails with bits cropped out of them. I thought the whole idea of a thumbnail was to give a mini representation of the image not an approximation.

Anyway I have solved my problem by editing the macro supplied by Imatch so that it can create all the required images and add which ever preset I want to the config.xml.

Imatch 5 is an image asset manager produced by Photools.com. It allows you to create each required jpeg size individually from a master uncompressed tif or psd file. I am a photographer and I organise all my images on an Imatch database.

I like the way juicebox displays on all the devices I have run it on - it is excellent! Would I be right in assuming that the 215kb js file contains some of the jquery library. Is there any way of optimising this overhead ?  On a bootstrap site you are already including the minified jQuery library at 95kb.