Yep - its down to the way the responsive site layout re-sizes pics for smartphone screens - - it actually makes the pics bigger than when they're displayed on pc screens which is a bit counter intuative,.. so all the pics that I'd r-sized & optimised for faster loading actually need to be replaced with higher res copies, which then get scaled down for bigger screens!!!

Big day on the glass today though, so it'll be morning before that's fixed!