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[Dendrocalamus64]

MyBB uses MyCode for markup.
https://docs.mybb.com/1.6/MyCode/

Code:

[img]https://upload.wikimedia.org/wikipedia/commons/thumb/5/5d/Pseudotsuga_japonica_togasawara04.jpg/282px-Pseudotsuga_japonica_togasawara04.jpg[/img]

yields



Or if you don't want it to be lost when the image host goes down or purges files, attach it, preview the post to get the URL, and use,

Code:

[img]https://forum.pine64.org/attachment.php?aid=1723[/img]

You can use the above image embedding code in other posts as well, you don't have to reattach it every time.