You're confusing hashing as in SHA-256 with perceptual hashing, which is more like a blurry thumbnail of an image converted into numbers. Any minor alteration

You're confusing hashing as in SHA-256 with perceptual hashing, which is more like a blurry thumbnail of an image converted into numbers. Any minor alteration to an image will change it's cryptographic hash completely, making those pretty poor tools for finding images that might want to be hidden. Perceptual hashing should match e.g. resized versions of the image, but with them two "blurry thumbnail hashes" can match accidentally.