I am using AI to generate illustrations. I am interested in illustrations without a discernible rectangular border. Few examples;

As a plus, there are elements on the edges which are complete but stick out of the overall boundary.

My images almost always have a rectangular edge.

The only question related to this that I could find is this, and I have gone through the suggestions, but it was not helpful.

What is this even called? What is this feature/style called? What are the keywords and/or prompt required?

I am using AI to generate illustrations. I am interested in illustrations without a discernible rectangular border. Few examples;

As a plus, there are elements on the edges which are complete but stick out of the overall boundary.

My images almost always have a rectangular edge.

The only question related to this that I could find is this, and I have gone through the suggestions, but it was not helpful.

What is this even called? What is this feature/style called? What keywords could I search for? Or what prompt is required?