On your web app, go to the left panel and click on Pictures. A page with the pictures taken will load up. Click on the download icon on the top-right of the pictures window, to download all the pictures in a zipped file.
You cannot export more than 1,000 pictures at a time
To Download specific picture(s), click on the picture to view Picture information (Timestamp, List Name, Item Name). On the information page, you have a download button at the top right corner.