You and your friend can share up to 300 photos at one time in a single Messenger window.
If you try to add more than 300 photos, a message will appear asking if you want to remove all of the currently shared photos and then add the new ones. If you don't want to remove all of them, just click "No," and then remove some of the photos to make room for new ones.
Where's the Contact Customer Care button? With so many improvements to Messenger since the version you're using (lots more features and reliability), we figured you're ready to move up. So get your upgrade and with the new version, rest assured if you have questions, you’ll find that friendly button on its help pages.