Image with arched edges

Arched edges is to introduce the pseudo elements :before and :after, size them relative to the container, and transform: rotate(-10deg);. Setting a hardcoded left and right ensures that the pseudo elements lie on top of where the image's shadow lies.

Arched edge shadows

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Rounded drop shadow

Here is another CSS technique for creating border shadows and dividers by utilizing curved CSS box shadows, the :before and :after pseudo-elements, and border radius.

CSS curved shadow

Source Code