Server gives 503 on almost all images

There are 3 reasons i think are producing this problem

1 - Something wrong with hosting , especially if your it is shared

2 - Someone trying to do a denial of service

3 - You have a lot of viewers in your server that the server is starting to get gradually slower

The 503 error means that the server can't serve up the image, not that it's not found on the server. 404 errors are not found. The fact that you're seeing both of these errors on your images is most likely the result of server resources being overloaded (as other answers have mentioned)...either capacity or bandwidth. If you're on shared hosting, this can happen often. Your site loaded fine for me just now, but of course, that can change the second your server gets bogged down.

A free cloudflare account is a good recommendation from Dan Web above...it will at least rule out the chance it's spam bots hogging up your resources.

Intermittent issues like this are almost always shared hosting problems. Your host will also rarely accept responsibility for the issues, and you're let with having to decide to move your site to a different hosting solution.