I frequently find that people have uploaded images from their phones and cameras directly into the image library and then added them to a page. What they have forgotten to do is optimise the image for the browser screen.
If I look at my camera, it takes image which are 5700px wide x 3800 px high and 10MB in size.
My monitor screen is a little higher definition than HD, so these images are too large for my browser, and if viewed on a phone which may be 700 pixels wide or less they are huge by comparison.
For most users these days, they view websites on mobile devices and may not be doing this over WiFi, so if they are downloading your web page from a 4G or 3G network, it is costing them money.
As a general guide your images need to be no bigger than 150kB in memory size, and no larger than the largest screen you are likely to come across. Today that is around 1200px for the web content space for most sites. Many of the sites I have built, the content area is no wider than 1080px. Continue reading Managing Images in WordPress