SceneKit - Diffuse png image on SCNPlane

In my project I'm trying to display some png images in my scene.

So I create a SCNPlane and I diffuse the image

    let image = UIImage(named: imageName)
    let node = SCNNode(geometry: SCNPlane(width: 10, height: 7))
    node.name = "elemets"
    
    node.geometry?.firstMaterial?.diffuse.contents = image
    
    self.mySceneBG.scene?.rootNode.addChildNode(node)

With this method I'm able to display the image in the scene, but the problem is the around the image there is a sort of "lights".

Please note the white border around the circle.

UPDATE

To be clearer, in this case I want to apply a round image in a rectangular plane.

The border I am talking about is highlighted in the green part

How can I solve this?

Thanks