Each English name describing a form of bird is referred to the one specific taxon that is the smallest unit of classification to which the image clearly refers. In the great majority of cases, a photo is referred to a species: for example, the Crissal Thrasher is referred to Toxostoma crissale.
However, there are both finer and coarser distinctions. Blue Goose is a color morph of the species Snow Goose; the base taxonomy system calls such groups “subspecific forms,” meaning that they are finer than species level; technically, “subspecies” has a narrower meaning in taxonomy.
There are many cases where the image is referred to a higher-ranked taxon than species. For example, “owl sp.” implies no finer level of detail than Order Strigiformes, the order of owls. Also, Consider hybrids such as Mallard (Anas platyrhynchos) × Gadwall (Anas strepera). This form is referred to genus Anas.