How to disable caching by nginx of files that are returned using a php script?

Question

Nginx

There is a URL like /avatar/id3/ , which returns an image, depending on the result of a certain condition, which is calculated inside the script. So, the problem is that nginx caches the first result and then constantly returns this image ( 304 Not modified ). How to solve this problem?
Nginx works as a proxy for Apache. Those. such config
location / {
proxy_pass http://*:7080;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
access_logoff;
}

Answer 1

location / {
proxy_pass http://*:7080;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
access_logoff;
expires off;
}