I mostly use my Ipad when on these forums, however, I do not use the mobile app. I found using the app limits you. I just saved cathe.com to my home page. Then click on forums. By doing this you should be looking at a screen exactly like you were using a desktop/laptop.
Not sure how it is starting a thread but right now as I am typing this I can scroll down and click on manage attachment under attach files.
Then at top left click on choose file then click on choose existing file (assuming picture is saved on ipad in your photos)once you click on picture it should bring you back. Click on upload on the right. Once file is uploaded scroll down and hit close window. Finish your message then submit reply and your picture should be in your message. Please keep in mind if your picture is too large it may not upload.
Hope this makes sense. Good luck!
I did a couple of screen shots as I was typing this. Not sure if all will show.