“Full” Screenshots and / or “other” image files. Re-sizing images for Forum posting / attachments - or display.
Elementary perhaps to some, to others… not so much.
Here’s a fullscreen
1920 x 1200 (El Capitan) screenshot of a desktop (re-sized in Photoshop for purposes here).
The original screenshot was
26.667 inches wide and
16.667 inches high! (@72 ppi). Much too large for posting here.

Now just imagine the above image at full original size on a 640x480 or 800x600 monitor!
Notice the default “Bicubic Smoother (best for enlargement)” Photoshop default for Resampling.
You don’t want that… very poor overall image quality & detail results when reducing size.
Instead,
Bilinear works best for most image reductions. (Actually used for image above.)

Notice that the overall file size was reduced from 6.59M to 1.12M
… when reducing first image to 11” x 6.875” size, from the original size of 26.667” x 16.667”
Still that’s large for Forum display and typically, prefer to keep images 9” wide or less.
But a 9” width here, “mucks up” the very small image details. Unreadable folder titles.
Seriously, how often does one need to show an entire desktop anyway?

Settings for the above 9” wide image.

A
Command + Shift + 4 selection… of a specific area - then Bilinear down-sized below.
Such an image capture, rotated 90˚ - and now you can actually read the folder name(s).

And images here are all “click-able” - to display their full sizes, per click.
Images initially displayed (or embedded within text) under 400 pixels wide - makes it easier for those on older machines… w/ smaller screens & display capabilities. If you’re only going to add images as attachments… reducing image file sizes or overall dimensions in this manner is also a good thing.
*Used Photoshop in all above examples but same /similar is possible with other image editing software apps. (Like Graphic Converter, etc.)
And now, to possibly mud-i-fy all of this a little bit more…Here’s a gratuitous image of the MotoGP GOAT!Valentino Rossi / The Doctor.
*And like all images it’s click-able to view full size. 864 x 1296

And here’s a reduction, also with Graphic Converter (small image inset - further reduced). Total size - 648 x 648

*This GOAT image used here without permission and may be removed upon request.
[Included here - also as something of a homage to “The Doctor”.]
Why all of this?Well it’s a precursor for a “how-to” concerning… text+picture+text embedding in Forum posts.