This question sounds easy, but it is not as simple as it sounds.
Brief summary of what\'s wrong
For an example, use this board; http://pinterest
You can trigger the json endpoint by making a request with this header: X-Requested-With:XMLHttpRequest
Try this in command in console:
curl -H "X-Requested-With:XMLHttpRequest" "http://pinterest.com/resource/CategoryFeedResource/get/?source_url=%2Fall%2Fgeek%2F&data=%7B%22options%22%3A%7B%22feed%22%3A%22geek%22%2C%22scope%22%3Anull%2C%22bookmarks%22%3A%5B%22Pz8xMzc3NjU4MjEyLjc0Xy0xfDE1ZjczYzc4YzNlNDg3M2YyNDQ4NGU1ZTczMmM0ZTQyYzBjMWFiMWNhYjRhMDRhYjg2MTYwMGVkNWQ0ZDg1MTY%3D%22%5D%2C%22is_category_feed%22%3Atrue%7D%2C%22context%22%3A%7B%22app_version%22%3A%22addc92b%22%7D%2C%22module%22%3A%7B%22name%22%3A%22GridItems%22%2C%22options%22%3A%7B%22scrollable%22%3Atrue%2C%22show_grid_footer%22%3Atrue%2C%22centered%22%3Atrue%2C%22reflow_all%22%3Atrue%2C%22virtualize%22%3Atrue%2C%22item_options%22%3A%7B%22show_pinner%22%3Atrue%2C%22show_pinned_from%22%3Afalse%2C%22show_board%22%3Atrue%2C%22show_via%22%3Afalse%7D%2C%22layout%22%3A%22variable_height%22%7D%7D%2C%22append%22%3Atrue%2C%22error_strategy%22%3A2%7D&module_path=App()%3EHeader()%3EDropdownButton()%3EDropdown()%3ECategoriesMenu(resource%3D%5Bobject+Object%5D%2C+name%3DCategoriesMenu%2C+resource%3DCategoriesResource(browsable%3Dtrue))&_=1377658213300" | python -mjson.tool
You will see the pin data in the outputted json. You should be able to parse it and grab the next images that you need.
As for this bit: &_=1377658213300
. I speculate that this is the id of the last pin of the previous list. You should be able to replace this on every call with the last pin from the previous response.