I was asked by many website owners why their website is loading so slow and they were worried there could be something wrong with their CMS or the server. To check the load time I use PageSpeed Tool from Google. This tool will analyse your website and gives you suggestions on how to improve the loading speed. Most of the times websites have the same issue which is the usage of large uncompressed images.
You can also read the RESS vs Responsive Design post about how to improve the speed for responsive websites.
Usually people use stock photos that have crazy resolutions. This is good because quality is important but depending on the devices used by the visitors, the quality of that HD image might be the same as a half resolution image. I think a FULL HD 1920×1080 image is enough at least for 2017.
Large images are not just slowing down your website but are also eating a visitor’s internet if he is using a mobile phone with limited internet. Google is also penalising slow websites and I think you don’t want that.
So, don’t forget to resize your images and reduce the resolution to save space on your server, reduce bandwidth usage, increase loading speed and avoid using all your visitor’s internet. Compressing an image does not necessarily mean it will also reduce its quality.