For stock, think beyond simple image quality. Strong subject matter and composition matter, but the image also needs to be sellable: common subjects are heavily saturated, so photos that are timely, distinctive, or harder to find can stand out.

Mood is also important because buyers often want images for marketing. Color, saturation, and sharpness all affect how the image feels—for example, soft focus can suggest a dreamlike mood, while low saturation can feel historic.

On the technical side, stock images generally need to be clean and well executed, but suitability also depends on legal and commercial usability. Avoid visible logos, trademarks, and other identifying branding unless allowed, since those can make an image unusable for commercial stock.

If people are identifiable, you’ll usually need model releases. Identifiable private property or certain notable buildings may also require a property release, depending on the subject and intended use.

In short: choose images that are technically solid, commercially useful, emotionally clear, legally clean, and different enough from the usual stock clichés to have a chance of selling.