This is my attempt to provide the essentials for inserting an image into a post. If you want more details there is a very long Thread about inserting images here
To display an image in a Post you need two things - the image must be hosted on some website and you need the URL for the image at that location.
You can host an image on other websites or you can upload the image as an attachment to your Arduino post.
Image uploaded as an attachment
If you upload the image as an attachment then you must go through a three-stage process to make the image appear.
First you must attach the image and submit your post.
If you find that your image is rejected by the Forum software see reply #27
Edit 20 September 2020
It is no longer necessary to follow through the second and third steps. Now when you submit your Post the image will automatically be made visible at the bottom of your Post. If you want it to appear at a different position you can Modify the Post and move the IMG link to the appropriate place.
Second you must view your post which will show the image name at the bottom like this.
If you right-click on the link and then click "Copy link address" you will have the URL for the image. You can paste that to your text editor if you want to look at it, but that is not normally necessary.
Third, edit your Post, position the cursor where you want the image to appear, click the image icon
and then paste the URL into the box. When you save the modified post the image should be visible.
The image icon just wraps
[img] [/img] around the image URL. For this test image it will look like this
The reader may also wish to read Reply #19 concerning Internet Explorer
Image from another website
If the image you want to display is already hosted on another website then to get its URL right-click on the image and click "Copy image address" and then continue with the third step while you are composing your Post
The full code for this external image is
Hope this helps
Edited 29 Dec 2017 to make the images easier to see and to correct one of the references
Edited 13 Apr 2019 to add reference to Reply #27
Edited 26 Jun 2020 to update the instructions for getting the URL of a link and existing image