d [read everything]

It' s clear : only the D letter ! no subjective meanings !
The mouth, the door and Adidas for exemple have no reason to be here, it's simple.
It's a challenge not so easy ...

it doesn't say you can't have other letters, though it does kind of defeat the point.

I don't understand the comments. It clearly states that the photo has to have the letter "d" in it. Noting more, nothing less...

Dear friends,
How can you find "photos with the letter "d" somewhere on it." if there is no other letters ?
Unless youtake a picture of the D key of your keyboard !!
it could be boring, though..

Ya, "only the letter "D" is pretty plain. I think the problem is many do not read or understand written English. The challenge host needs to keep the rules very simple so those who don't read English well will have an understanding.
This kind of a challenge stating a photo with only the letter "D" is impractical for most anyway. Can't search through your archives for this challenge, you must go out and search the letter 'D" and then do some PP cropping if need be. Anyway, that is my take on it.