This comes up regularly. Just copying and pasting does nowt, it need to be in a format the forum software will recognise and incorporate into the text.
Sign up for a photo-hosting web site, I use Post Image, you can sign up for free or a paid account and go ad-free if their spamverts annoy you (these don't show up in your actual posting, so it doesn't bother me). Other sites are available.
https://postimages.org/Signed up? OK, upload your photos,
it will give you a re-sizing option which you will need to keep the photos being too large, eh Ben?
640 x 480 or 800 x 600 will do. Expiry date or none is up to you. Select the graphics file of the picture you want to upload,eg something like DSCF4539.jpg and upload.
The next bit is where people always seem to struggle. If on the hosting website you now click on your upload it should go to a page with a whole list of different types of sharing code depending on where and how you want to share your picture.
If you're using Post Image the one you want is called
Hotlink for forums. Find THAT link, IGNORE ALL THE OTHERS.
Got it? Copy it and paste it into the message you're typing on this forum, remember it needs to be on a new, separate line from the rest of the text.
Now when you preview your message the picture should come up, as it will when you post the message.
A.