Visual memory can be long term or short term, or visual memory describes the type of memory that is short term or long term. This is why visual memory does not equate short term memory; they don't mean the same thing. E.g. the definition of "apple" is not the same as the definition of "fruit". It is confusing when you think it in terms of "apple is fruit", but give this a logical analysis and say fruit is the universal set of apples, oranges, ..., and etc., while the universal set of all apples are macintosh, albany, ..., and etc(mathematics of set theory), thus the sets are different due to the things that they define.
Quotes from Mastering The World of Psychology (3rd edition):
"For encoded information to be stored, some physiological change must take place in the brain--a process called consolidation..." -pg 178
"If information is processed effectively in short-term memory, it makes its way to long-term memory..." -pg 182
"Information in long-term memory is usually stored in semantic form, although visual images, sounds, and odors can be stored as well..." -pg 182