Is there a way to like fit the skeleton graphic inside the image?
How to mask an image using skeleton graphic?
I'll briefly chime in to suggest this blog post, which may have an example of what you are after based on the title of your thread:
http://esotericsoftware.com/blog/Unity-SpriteMask-and-RectMask2D-support#Unity-UI---Rect-masks-and-SkeletonGraphic
Thank you @Erika