How to make a "one-time redirect" in nginx?

Question

Nginx

on the first call,
site1.ru/1.jpg -> redirect 301 site2.ru/2.jpg
on the second+ call, the redirect should not occur,
tell me the finished version?

Answer 1

location =/1.jpg {
if ( $cookie_megablah = "" ) {
add_header Set-Cookie megablah=1;
return 301 site2.ru/2.jpg;
}
root ...;
etc;
}
Fix the syntax yourself, I think.

Answer 2

I couldn't make it myself, can you tell me how it should look like?