There area couple of options rather than taking photos at low quality/low resolution.
...if you lower your camera's resolution, then the next time you want to take HQ photos, you'll need to change it back.
Or, you forget, and all those lovely vacation photos are crap, because you forgot to adjust your camera!
I always take photos at the highest quality setting my cameras can offer.
I then edit those photos and usually save the original as well as the edited version.
The first edit I apply is adjusting the size of the image to suit my needs.
Some photos are used elsewhere so I want to retain a higher resolution version,
and so I want to keep the original for those uses.
But for Forum posting, I stick to 800px wide
(usually 72dpi, no higher than 300dpi)
Anything larger than that can't be fully viewed within the confines of the forum layout
or on smaller screens like tablets and phones.
If you are using an online photo storage site, it may offer an upload setting
where whatever photo you upload is automatically resized to a set resolution.
The evil Photobucket (lol) offers this option, as do other image galleries.
Check to see what your service offers first.
But if you are using this Forum's attachment option, you must resize your photos before upload.
So whats an easy solution to this?
Heres one that I use:
https://www.fotosizer.com/
Its a free program...pretty basic.
Theres a Pro version that you can pay for that has more options.
I've been using it for years and works very well.
The basic version does not have ads or anything annoying..and does not watermark your images.
You can preset a number of output settings or change them each time you do a resize.
You can drag and drop one, or many photos, into the main window and then apply the resize to all.
As well as presetting the pixel resolution output, you can reduce overall quality including dpi (if necessary).
Most point and shoot cameras store jpegs at 72dpi so this isn't usually an issue
Downsizing the image (pixel wise) usually does the trick for Forum posting.
You can even apply some filtering effects with Fotosizer.
Its designed for "batch" editing....but I often just resize one photo.
It has the advantage of very quick program load, and simple operation.
Easier to use than my bigger Graphics/Photo editor software.
It also does not delete your original photo...you can specify the output location for resized photos
(I often just leave them in the same location with the original)
but it creates a new photo with a generic name (Photo 1, 2, 3 etc ...you can rename yourself).