You can use craigslist to host the picture. Just post an add and upload your picture. You can get an image link on the iphone by clicking the picture and copying the url to the post. then wrap with tags.
Here's a guitar I have on my local craigslist as an example...
[img]https://images.craigslist.org/01111_fU0kIB9h5h5_600x450.jpg