PowerPoint allows you to draw curves as lines, but it is harder to make fills under a curved line without resorting to actual data charts. Here is what I do: I use rectangular shapes to cut/shave a shape. See below. Notice that it is also possible to fill your custom shapes with images.

 Draw a shape

Draw a shape

 Position your knife

Position your knife

 Use the "subtract" function to cut the shape

Use the "subtract" function to cut the shape

 Horizontal knife

Horizontal knife

 One more cut

One more cut

 Fix the edges with format shape - edit shape - edit points

Fix the edges with format shape - edit shape - edit points

 Add an image if you want

Add an image if you want

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