This effect creates gradual darkening of the image towards the corner, i.e. vignetting, to give a look as if it is taken with a toy camera. Color hue can be adjusted.

Here are some examples

The toy effect makes it look as though the teddy bear is walking by itself.

A peek-in feel can be created to a huddle of kitten toys.

A bike on the side of a road is given a nostalgic feel.