How allowing img tag in formats can be dangerous?

Question

I get this recommendation form Security review module:

It is recommended you remove the following tags from roles accessible by untrusted users: img

I am wondering what real world threats can img pose?

Answer 1

Project page of security review module says

Text formats don't allow dangerous tags (protecting against XSS)

Cross-Site Scripting (XSS) attacks are a type of injection, in which malicious scripts are injected into otherwise benign and trusted web sites. XSS attacks occur when an attacker uses a web application to send malicious code, generally in the form of a browser side script, to a different end user. Flaws that allow these attacks to succeed are quite widespread and occur anywhere a web application uses input from a user within the output it generates without validating or encoding it.

An attacker can use XSS to send a malicious script to an unsuspecting user. The end user’s browser has no way to know that the script should not be trusted, and will execute the script. Because it thinks the script came from a trusted source, the malicious script can access any cookies, session tokens, or other sensitive information retained by the browser and used with that site. These scripts can even rewrite the content of the HTML page.

For example you can use img tag as below for XSS attack..

<img src='#' onerror=alert(1) />