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It's easiest to do it in markdown. To do that, you should go to http://imgsafe.org/ and upload your photo and then use the link from the photo in markdown. See how to add an image in markdown here.

http://imgur.com is another site to use. Just in case http://imgsafe.org is down.

There is also a new Steemit photo hosting site that is really quite nice.
Link: https://www.steemimg.com/
If you like it give the person a vote: https://steemit.com/steemit/@blueorgy/steemimg-com-first-dedicated-steem-image-hosting-website