Thanks guys for your input.
So, I cheated.....
I wrote a script to rename any image.JPG to image.jpg.... very poor solution I know! But it worked! and pretty fast too. I probably should re-write my search to use the search files function, and may well do so. The photos only change rarely, but it would be good to cover this possibility.
I am serving the images from drive Clark - it's great - but unfortunately, you do have to make the file accessible by anyone on the internet and give them view permissions, not a huge problem as the fileID can't really be guessed, but still not ideal.
Thanks again for the assistance.
Laurie