How do I get a photo inside a custom shape in CS6...
Also, in Sharon's method - "simply press delete" on a regular jpg picture will bring up the Fill Dialog in CS6, with Content Aware being default. Not what you you want here.
If the OP wants to use a selection as a "custom shape", then creating a mask by clicking on the Add a Mask icon at the bottom of Layer panel (third in from left) is preferable to inverting the selection and deleting pixels.
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