I was making a post on the gamedev meta and after I posted it I noticed that between the Header and the image I first uploaded there was a trailing [ and I went to edit the post and remove it, only...
...it doesn't actually exist, except as part of the image embed markup.
Blue to notate the original image (and scribble over the original freehand circle).
As noted in the comments, you're missing a ] before the first [1] (which you presumably deleted by mistake).
[text][number] is a link.
![text][number] is an inline image.
Putting the two together (by replacing the "text" part of the link with an image, to make an image with a link) gives you [![text][number]][number].
In your case, apart from the extra [, this would mean the image isn't also a link, as the text of the image is text[number] instead of just text, and the last [number] is consumed for the image, and is thus not available to make a link.
You can also use the alternative form [text](url) in any of the 3 cases above (although in the last case that would require the URL appearing twice rather than just having it once with 2 references to it).
on. Since that isn't the default image description, I assume you deleted that bracket by mistake when typing up the description.