I did it on my tablet. Not sure if its the same for an iPad but...

Go to the image in your gallery,
Bring up the menu for the image - on my tablet I touch and hold the photo until it shows the menu
Click view image
And copy and paste the web address from the bar at the top
Into this text box and add [img] to the start and [/img] on the end.

Hope that makes sense. Lol it does to me, but I already know how to do it!