I'm not sure what you mean by write up. Do you mean an article to accompany the images, or a cover/query letter? You need to do exactly what the submission guidelines suggest, or risk having it all thrown in the trash without a look. If they say query with samples, that's what you do. If they say no unsolicited submissions, you don't submit unsolicited. Its 99.99% how you present yourself (not the pictures) because if you don't pass the eye test they won't even pay attention what you sent. So whatever you are asking here, the answer is going to be specific to the magazine you want to submit to. There is no generic, one size fits all answer.
Maybe its different outside the US, but that's how it is here.
Sent out few emails to the best known magazines. The problem is that most of them don't even have submission procedures to follow so it's a bit of a guesswork whom to send it to.
Well, we'll see.