Yes and no. If you are thinking about cryptographically-secure hashes, then you're correct. However, not all hashes are intended to be cryptographically secure;

Yes and no. If you are thinking about cryptographically-secure hashes, then you're correct. However, not all hashes are intended to be cryptographically secure; this particular kind of hash is called a perceptual hash. Perceptual hashes are specifically intended to be able to identify slightly-modified images; and for that purpose we can't have all of the cryptographic security of, say, SHA-256. The third type of hashing is the dirt-simple hashing schemes you see used in hash tables; although even there denial-of-service resistance is still a desired property for public-facing web services.