microdot

详细解释:a. 微粒的
n. 微粒照片, 小粒 *

英语解释：

名词 microdot:

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

详细解释：

mi.cro.dot

n.（名词）
A copy or photograph that has been reduced to an extremely small size for ease of transport and purposes of security.
微粒照片：为易于运送或保密而将印刷品或照片缩小至极小尺寸的照片