A little late to seeing this, while this is a “solution” it’s not a proper one.
That forces the image quality to 420x420. If the image you want to use is already 420x420 or below, then I suppose it’s fine but in most cases these days people use 512x512 or the Roblox maximum 1024x1024 [if you upload an image above 1024x1024, it downscales to 1024x1024]
It used to be quite easy to tell someone “just remove 1 from the number of the item” but now things have gotten much harder because the difference between Image and Decal are so far apart.
While I use the method you linked to above for when someone uploads a car texture to my game as a Decal ID rather than an Image ID, it’s extremely noticeable which one is which.
These days I resort to telling people to “get the number from Studio” [as it’s the easiest way to describe how to obtain the Image ID] but users who don’t own a computer or have never opened Studio have no idea what to do.
As a Roblox developer, it is currently too hard to get user generated images into your game without having to hassle your users to find “the right ID” to use.
Crazy to see I’ve had the same gripe for 4 years now.