Hear hear! The apostrophe used to denote plurals is very irritating.
"Buff" is not an abbreviation of anything. It is an informal noun meaning an expert on or devotee of a given subject. It originated in the US, where it meant "an enthusiastic fire-watcher", from the buff-coloured uniforms worn by volunteer firemen in New York City.
Even if it were an abbreviation, it would not warrant the apostrophe. The plural of photo is photos. QED.