There is no verb in the sentence. If we add 'tomo/hizo' (took), we get:
Quien (tomo/hizo) las fotos de la fiesta = Who (took)the photos of the party
los fotos = the photos
"¿Quién va a la fiesta?" means "Who is going to the party?"
It means, "For whom is the party?"
"De quien" means from who?; "De quien(?)-whose(?)";
"De quien" means "from whom"
Con quien means "with whom"
"Who are you with?"
Who is that
"Quiem" is not a word in Spanish or English. "Quién" is a Spanish word that means "Who" in English.
Translated to English from its Spanish origin, fotos de caballos means "photos of horses". There are thousands of photos of horses online to look at.
it means THANKS FOR THE PICTURES
It means Who knows