Image to be shown on one tap on iOS?
There might be a better way to do this, but this should work.

Upload the image to imgur.com. Then get the direct link to the image (it will look something like http://i.imgur.com/ipB4C6r.png). Open that url in Safari on your phone, hit the Share button at the bottom of the screen (the box with the arrow pointing up) and hit "Add to Home Screen."