I've seen it happens many times where people go about trying to add in DOF and motion blur in post, and it ends up with this ugly, blurry outline. This is caused by whatever objects are in focus being blurred in the background, causing just the edges to peek out around the in-focus layer. The ugly effect in question:
Here's how to get around all that.
Plus a bonus.
It's a pretty long process, especially for very complex images, but it's worth it. Original image by HairyBastard. I did the edit in the Official Edit My Screenshot Thread V6. My original version can be found here.

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