Sharing here my personal experience with Facebook photos displaying “content not found” for photos and images URI issues.
Original or old Facebook photo link that you used on your Website or blog that no longer works because Facebook keeps changing their CDN and image servers:
New link to that old image:
Original Facebook image URI: https://fbcdn-sphotos-a.akamaihd.net/hphotos-ak-ash4/251959_10150994404484776_172973847_n.jpg
New Facebook image URI (as of March 2016): https://scontent-mrs1-1.xx.fbcdn.net/hphotos-xpa1/v/t1.0-9/251959_10150994404484776_172973847_n.jpg?oh=9be182a1c481d21242f9ca279276ec11&oe=5784232F
We see that main domains of Facebook server containing pictures previously was akamaihd.net and now it’s fbcdn.net – things are obviously. Try your luck manipulating image or photo URIs.