Recursive Apple ID password procedure?
First, just clearing my doubt, did he try checking the mail in a popular browser or any device? , just a guess, may be due to the browser agent, he might not be able to view the image or link. 

Now if this is not working he has another option to use the secret question option. If he doesn't remember that , just ask him to mail apple support with his mail id and username ,and they can help you , they really do too..