I have written several online publishing wizards in my day.
As a rule, for all my ES posts I set the image height to 340px @ 96 dpi. Some of the images are longer than 1920px (panoramas) and when they do, I post a link to the full image and let the Browser handle it.
IMO - 2048 is too wide for this forum. Actually - so is 1920px for many people with older computers. 1080 is passé; 1280 is the new minimum, with 1600 the new nom.
Another aspect to consider aside from H & W, and that's dpi: Some people have no idea of image management, and simply taking the extra step to reduce the dpi from 300 or 180 down to 96 will chop the file size down to a fraction without ever impairing viewing quality.
Finally there is image compression: The rule of thumb is that if the image is from nature (people, plants, sea & sky) use JPG at 60-80%. If it's graphics (charts, text, drawings) use PNG.
There are scripts that can be written which evaluate the four dimensions and optionally create a thumbnail placeholder. I don't write in php - however this is a no-brainer in the .NET world.
Resized to fit, KF