if you have a line around your render (usually when there is a light background) here is a fast and easy way to get rid of it once your done cutting out the render: right click on the layer select blending options select the inner glow option change the color to black change the blend mode to normal and select the smallest size (puts an almost undetectable black line around your render) and your done you could also "defringe" your render but i find that it ruins all the edges of the render, not just the light outline
here u go Dr.J i fixed up Jims really bad white outline cloud with cellphone render and done this to it:
