All images served on lonelyplanet.com should be in the most efficient format as well as losslessly optimised . You can losslessly optimise images manually using these tools:
We have a contract with a 3rd party image API which can resize, crop, optimise your images on the fly. The only caveat is that the images need to be stored on a Lonely Planet domain. There is a helper within Rizzo that abstracts some of the complexity around this service. For full documentation you can visit the resrc.it docs.