This is quick post about Last-Modified header. Please imagine following situation: you have image stored in your database and you need to send it to the browser on some request. But image extraction from database takes some time, and if there are more than one image you Web-server’s productivity will decrease dramatically. Is this case you need to implement caching functionality in your application. All images can be changed therefor you need to have ability to check image modified date (for example, this date can be stored in same database).