Your browser (for example firefox) and the management of HTTP 401 status/error code
The Hyper Text Transfer Protocol defines various status codes/error codes.
Amongst them, the most frequent are the 200 code (OK: no error), the 404 error (document not found) and the 301/302 redirections.
There is also the 401 status, which is used for HTTP Authentication.
The server may return the 401 status code when you try to access a page, but also when your browser try to access images embed in a page with the img tag. This blog post deals with some unwanted browser behaviour that may occur with “images” returning a 401 status code. Read more »