If you want to download pictures from internet its easy as right clicking on it -> Save Image as But if you want to download lots of pictures like facebook album it wont be easy to right click on every one and saving it.
There are many apps,software’s are designed to help you with this issue. One is FBdownloader  thats the most popular one but I found that its not convenient as it should be. You should give your fb login credentials to use it and you can only download your frinds photos and your photos but even to download your friends photo albums, they must have set the albums are public and even when you can view it on web browser fbdownloader wont allow to download photo albums of your friends if they marked them as “Private” or “Friends only” .  So its not a good option.
And when I was searching for the most convenient and easy solution I found great Google Chrome extension for doing this.