I think attaching a picture on anywhere that needs to look into your iPhone directory is impossible. Simply because it's Apple LOL. It's true, for instance, you can't go on PicPaste and put a picture on there via Apple products. Android is possible because it's pretty much has the interface like a computer.
Solutions? Upload it using your computer/laptop or use an android phone/tablet
Another solution, if you need need to host a picture up is use Photobucket, they have an app for free in the App Store, very simple to upload it up but setting RA will be impossible, unless a mod saves the picture and edits your post + sets RA rating himself.
Hope that helps!