Interesting posts and I do understand why you have done this, so kudos for trying to encourage others on how to use their "camera" and software to adjust the image sizes.
As an addition to your excellent posts I would say that folks can often over complicate their own attempts by looking for free software or putting the images online with access to others and so on...
Your suggestion to use the basic "Paint" programme in Windows (not Paint 3D) is by far the best as it is the easiest way to get the images down to size.
Using jpeg format is the default and folks should check they are actually using this, if not, again use "Paint" and "save as" in the "File" menu to check they are using the jpeg format which uses smaller file sizes than other formats.
Incidentally jpg or . jpeg stands for "Joint Photographic Experts Group", which is the name of the group who created the JPEG standard....
Others are bmp, tif, or tff and png.
Of course one can also check ones camera, or mobile camera, as there is often an opportunity change a setting to take pictures in a smaller format, as low as the good old fashioned 640x480 which was the default for years..... before HD came around!
This can often only be seen on digital cameras as image size in Megabytes (Mb) and some experimentation is needed to find the optimum smaller image size for use on web site related uploads.
Using this option can remove the need to manipulate image files before uploading.... but remember if you want to take pictures to later print them off for framing, then higher resolution is better so more Mb's in the camera setup are required.
This will obviously mean more work as previously mentioned to reduce them for upload to the forum.
Using 4:3 format or "square" format, can reduce sizes more quickly. The 16:9, or widescreen style image will always use more Mb, much more!
I am not trying to teach those who know all this to suck eggs, but having had a very early digital camera bought in Hong Kong and having been in I.T. I do know that a lot of folks do struggle with technology!
This I am painfully aware of for two main reasons, firstly, my wife is an absolute technophobe, secondly my son has a Masters degree in Network Security, making me feel like the gopher grade IT assistant......
It would be interesting to hear what issues others have in relation to this topic!