Photos: Add the ability for folks to share how they used a photo and to have that sent to the photo contributor

[annezazu]

I submit photos to Pexels and, from time to time, get emails from them about how a photo I submitted was used. The feedback is shared from the person who downloaded it so I imagine there are a few steps here:

1. Offer the option to share how you plan to use the photo you downloaded when downloading a photo from the directory.
2. Have moderators review these messages and decide whether to send it to the photo contributor.
3. Send the email to the contributor with the message about how the photo was used.

Personally, I found this to be a really lovely feedback loop to share more with Pexels (although now I'm biased towards the WP Photo Directory) :)