There is no limit on number of photos that you work with in Flickr Batch Organize. The application can handle as many as 150 - 200 (or more) photos in a batch. However, the number of images that you can work within one batch may be limited by your Internet connection. You may face a slow process between your computer, your Internet service provider (ISP) and Flickr servers. If you encounter any fail uploads while processing large batches, consider uploading pictures in smaller batches. As there is no set limit, you'll have to experiment with a number of pictures to see what works best for your connection.