I will keep images below 1024px max dimension and that should do it.
Agreed, that’s definitely old school in terms of what even the most basic smart phone is now capable of…
Well, the dimensions can be larger than that, but that's one approach.
When I post pics here, I do some experimentation, For instance, the way I have my phone set up, my default pics are 4032 x 2268 x 24. (That's a 16 x 9 ratio pic.) I just looked at a recent one, and my Mac lists it as 2.7 MB (but pic sizes will of course vary a bit).
Now, if I use some software that I often use (in my case, XnViewMP) and resize it by half -- 2016 x 1134 -- it results, for that particular image, in a nice clear pic with a size of 422 KB, i.e., less than half the limit here. Here's that resized pic (I was discussing the rear seat on my Royal Enfield in an email exchange with someone):
Note also that the limit here is not
completely old-school, old-timey, etc. If you've ever put up a video on YouTube (at least the free YT account that I have), you know that there's a thumbnail/initial screen that YT requires. It will do this itself by default, i.e., pick some "cel" in the video by some formula, and go with that. I'm talking about what you might call an "album cover" if we were talking about LPs.
However, if you want to add the thumbnail/initial view yourself -- typically, pick some screen grab from the video -- you will get an error if that image is too large: the error message states that the max size for the "album cover" type of thing is ... 1 MB! (Unlike this forum, YT actually allows you to go larger, approaching 2 MB, but that's the error message you get.)
EDIT ADDITION:
I just realized that XnViewMP, the software that I mentioned, is also available for Windows (and UNIX). It's free for non-commercial use, and I've been using it for years (on my Mac) for basic photo editing, such as cropping and resizing. Highly recommended (especially at that price):
XnView, one of the best and popular image viewer. It allows you to view, manage, resize and edit your photos.
www.xnview.com