Use humanoid.HealthChanged to make the text say -10 depending on health taken.
Also if you uploaded the images recently, it has to pass moderation first.
Check this post if your image was not recently made: Can't seem to load image - #2 by rogchamp
Also I think 2 years ago I had the same issue with changing decal ID, my solution was literally just make multiple imageframes and turning their visibility on/off when I want to use the specific image. (Rather than changing the id)