MICRODOT

microdot

(noun) photograph reduced to the size of a dot (usually for purposes of security)

Source: WordNet® 3.1

Etymology

Noun

microdot (plural microdots)

A text or photographic image that has been reduced in size to that of a typographical dot in order to escape detection by unintended recipients.

(informal) A small-sized tablet containing lysergic acid diethylamide (LSD).

Verb

microdot (third-person singular simple present microdots, present participle microdotting, simple past and past participle microdotted)

(transitive) To make a microdot of.

Source: Wiktionary