www.w3schools.com/browsers/browsers_display.asp and http://gs.statcounter.com/ are two sources of global web site statistics. The statistics in each are dependent on the particular subset of all users reflected in their statistics.
The former indicates that from 2011-2016, 97% of users have a screen resolution of 1024x768 or higher. The fact that this figure has gone down in 2017 and 2018 probably reflects the increased use of mobile devices which generally have smaller screen resolutions.
The W3school site notes that "W3Schools' statistics may not be relevant to your web site. Different sites attract different audiences. Some web sites attract developers using professional hardware, while other sites attract hobbyists using older computers." Visitors to the W3schools website are looking up information about html tags, css properties, JavaScript, and other web technologies and are likely using desktops or laptops for this purpose.
| Camera | Pixels | Source |
| IPhone 4S (introduced in 2011) | 3,264 x 2,448 | http://en.wikipedia.org/wiki/IPhone_4S |
| IPhone 4 (introduced in 2011) | 2592 × 1936 | http://en.wikipedia.org/wiki/IPhone |
| Olympus Tough TG-310 (2011 camera) | 4288 x 3216 | https://www.digicamdb.com/specs/olympus_tg-310/ |
Thus these smartphones and cameras, introduced in 2011, produce pictures whose pixels exceed the screen resolutions of computers and whose file size is too large for common use on websites, and thus image optimization (reducing the number of pixels and file size) is required.
Revised: September 19, 2018