Do your forum a favour...
reduce the (data) size of your images before you upload.
Maybe the forum has a resizing protocol in place, in that case it probably doesn't matter.
Images take up a lot of storage space and I know of many forums that ran into a problem running out of storage space because of attachment sizes.
Personally I have always reduced the size of my images before storing them online, or uploading them to a forum like this one.
Photos right out of my Nikon are quite large.
Even my smartphone shoots fair size images (on high quality).
I use a simple (free) program to handle resizing.
Its called Fotosizer - get it here:
https://www.fotosizer.com/
You can quickly resize one photo at a time, or dozens all at once (its called batch resizing).
I have a simple tutorial on how to use Fotosizer for just this purpose,
but it's on my own modellers forum which can only be viewed by members.
If you or others are interested, I would be willing to copy it over here. (it has pictures! lol)
But I won't do that before I hear comments.