This subject has come up several times and AFAIK here's why it happens.
The "distorted" images have the X and Y-axis values reversed due to EXIF rotation.

There appear to be two issues here:
1. A while back, Saint mentioned that newer images embed orientation/rotation info in the EXIF metadata, but the process of importing/translating EXIF metadata creates a confirmed exploitable security hole in the forum software plugin.
2. The forum's image handling plugin appears to have trouble automatically handling links to images over 1024 pixels wide that have EXIF rotation -- fortunately you can use "width=" and/or "height=" to make those images display properly.
In the post
here, the embedded image shows a resolution of 4032x3024 -- 4032 wide x 3024 tall.
[img]http://forum.arcadecontrols.com/index.php?action=dlattach;topic=160205.0;attach=383549;image[/img]

You can display the image properly by swapping the width and height. (simulates the EXIF rotation)
[img width=3024 height=4032]http://forum.arcadecontrols.com/index.php?action=dlattach;topic=160205.0;attach=383549;image[/img]
orIf you single-axis (height or width) scale the image width to 1024 or narrower , it seems to display properly.

[img width=1024]http://forum.arcadecontrols.com/index.php?action=dlattach;topic=160205.0;attach=383549;image[/img]

The reason I mention 1024 or lower is because if you try to single-axis (height or width) scale the image width to 1025 or wider, the forum software auto-resizes and distorts it.
You type in . . .
[img width=1025]http://forum.arcadecontrols.com/index.php?action=dlattach;topic=160205.0;attach=383549;image[/img]
. . . the forum software changes it to . . .
[img width=1024 height=767]http://forum.arcadecontrols.com/index.php?action=dlattach;topic=160205.0;attach=383549;image[/img]
. . . which displays like this.

Good news: You don't need to re-define the width on smaller images.
Notice that the 3rd image uploaded to
this post is distorted, but when you put the URL in the "img" tags . . .
[img]http://forum.arcadecontrols.com/index.php?action=dlattach;topic=160205.0;attach=377050;image[/img]

I'd say the easiest workaround is to upload your images to the current
Not a Project thread (who cares if they look distorted in that thread

) then use those image URLs in your thread.
- Remember to re-define the width as 1024 or less for any larger images that appear distorted in the "Not a Project" thread
or dual-axis scale the image. (swap the height and width values)
Scott