How to add a picture sent from email to my photo gallery on iPhone?

Someone sent me a photo I want to upload to Instagram, but how do I get it in my gallery!

If it's not your photo then you have no business uploading it to Instagram in the first place.

Whatever is 100% correct.

You need to learn to respect others property.

Just post photos you take with your camera.

I believe that actually breaks the terms of service for using Instagram. It's supposed to be for sharing your own photos taken on your own phone. You could end up with your account getting closed down for posting copyrighted images.

If there's another person involved, tell them to get their own instagram account, and they can post their own images.