I remember making an image like this some time ago. Back then, the Blank Template did not impose the 20:1 aspect ratio limit.
While it didn't have a message reminding you of the limit, Imgflip still could not generate images within a certain range. The highest aspect ratio that Imgflip could generate was a 1000:8 image.
Here's the image:
imgflip.com/i/6z670i
