creating silhouettes

Here's how to make a clipping mask in Photoshop. Using the object selection tool. You can also use the magic wand or what ever is appropriate. WHen you have the selection the video show how to make a clipping path, but you can also use it to make a layer mask https://youtu.be/nW9RjbUwhQk

You could make a layers mask like this. https://youtu.be/eWw-z_ydxlc

If you cannot find a suitable channel, choose the best you have, duplicate it and increase the contrast using Levels or curves. In order to turn a channel into a selection, cmd click it (ctrl click on Windows)

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Always keep a backup of (versions of) your artwork, especially up to irreversible changes.

Depending on the exact nature of the artwork, you may be able to obtain the desired appearance with the help of a set of two background ractangles, a black one on top of a white one.

If the outer bounds of your artwork parts consist or can be changed to consist of filled paths, you can turn those filled paths into a Compound Path and apply that to the black rectangle, thereby making those parts (of the black rectangle) appear as silhouettes on top of the white rectangle.

In many cases, whether vector artwork and/or raster images/effect, you may have one or more (quite different) options to turn them black or white (in appearance), and use them as a Group for a(n Opacity) Mask along with the black rectangle with Clip ticked and Invert Mask ticked or unticked.

With either approach, those parts (of the black rectangle) will appear as silhouettes on top of the white rectangle.

You can get a first impression of the former here,

https://helpx.adobe.com/illustrator/using/clipping-masks.html

You can get a first impression of the latter here,

https://helpx.adobe.com/illustrator/using/transparency-blending-modes.html