Your Image Gallery is a thread. You can add 8 images per post. If you have 24 images to upload, just upload he first 8, that starts the thread, then under the Quick Reply box click Use Full Editor and repeat the process to upload images in the first reply. Then repeat for the last eight images.
You should then end up with 8 images in the original post that started your Galley, and two "replies" each with 8 images.
You can add as many as you'd like in subsequent replies.
