Note for sharing photos here I'd recommend using Google Photos or Facebook, as the pictures won't really "expire" so people can see them for years to come.
When posting on the forums, you should see a window similar to the following:
Click the "Img" button as circled in the picture. A set of brackets should come up on your post. Inside the picture, put the URL of the picture you would like to share.
To get the URL of your picture on Google Photos:
-Open up your picture, click the "Share" button up at the top right, the leftmost icon
-Click the "Get link" button (Don't use this link as it won't show up on your post)
-Open the generated link in your web browser
-on this page, right click and open the image("View Image" on Firefox)
-copy this link, this is the link to the picture
Be sure to make use of the "PREVIEW" button before finalizing your post with the "SUBMIT" button