DOP,
Cartridge casings will typically have a head stamp (on the bottom if they're standing up like in your photo) identifying the maker and the cartridge.
Measurements of the overall casing length and width at the base, shoulder and opening, can be helpful if the head stamp isn't readable. Additional information can be gleaned from the location of the firing pin strike (along the edge of the rim or in the center).
Rich
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Just One More Good Target Before I Go . . . .
800 - Deus