How does it a product to put a picture of it on a t-shirt?

it might catch someone attention and ask the person with the shirt on about who made it how can i get one and stuff like that you're basically promoting the product to gain popularity so the product can get more customers which also mean more money

artists followed a set of rules to achieve ideal proportion.

soft,hard and rough for soft would be a pillow or a stuffed animal hard wood floor or a table rough paint