The other option is to do this
Instructions for Imgbb. 'For guests'
https://imgbb.com
,
1. Click "start uploading" usually a blue tab
2. Select an image saved on your phone or computer.
3. Click "Upload" that's usually a green tab
4. Choose "BBCode full linked" from the drop down menu in the upper box.
5. Click the link provided in the lower box. This should highlight the link.
6. Click on 'copy' in the top right corner of the lower box.
7. Then paste the link into a new post you've created on the forum.
The above instructions are assuming you are a guest on imgbb, and to start with that is better.
Once a signed in user on Imgbb, I found 'BBCode full linked' produced a very large photos on the forum and selected 'BBCode medium linked' in most cases instead.
Any problems just ask.
Good luck.
Tommo
