All "alt" attributes for img elements should be clear and concise. "Alt" attributes over 100 characters long should be reviewed to see if they are too long.

Example

Wrong

<img src="dog.jpg" alt="A photograph of my very, very, very special dog whom I love so much. He is a very good dog, a loving dog, and my constant companion these many years. Yes, all agree, my dog is a good dog.">

Right

<img src="dog.jpg" alt="A photograph of a dog">