Designs that has pictures taking up the entire width of the screen

So there are many websites where a photo will take up the width of the screen. Some have the photo taking up the entire monitor. How do you decide what should be the max width of the photo given that more and more people have monitors that go beyond the average width, of say 1600px?

You can use media queries to sense the size of the screen to then serve an image of an appropriated width.

if i use a large backround, I make it 1050 px wide and i let it fade out to white (the pages background-color ). For now I would not go larger than 1050 since my analytics say tat is the best size.

But this really depends on what you are designing.

Keep in mind: the larger the pic the longer it takes to download it.