I am trying to work out how cookies are being set on a website, I have scoured the page source and can see how most of them are being generated.
However, there is one cookie that appears on page load that I can't track down.
Is it possible that a cookie is being set when an image is being requested from a remote server? If so, can I inspect that http request response with a tool to find out if it contains the cookie?
Any HTTP-Request can set a cookie, if the server says so.
Cookies are set using the Set-Cookie HTTP header, sent in an HTTP response from the web server.
A request for an image is basically the same as a request for a html page. It uses the same request/response structure. So yes you can set a cookie on an image request.
The request/response can be seen in most modern browsers. In FireFox there is under tools -> Web Developer -> Network a tool that shows the requests/responses from all calls being made on a page. Opera and Chrome have similar functionality.
