When uploading multimedia data such as photos or videos on social network
services, websites, and so on, certain parts of the human body or personal
information are often exposed. Therefore, it is frequent that the face of a
person is blurred out to protect the portrait right of a particular person,
and that repulsive objects are covered with mosaic blocks to prevent others
from feeling disgusted. In this paper, an algorithm that detects mosaic
regions blurring out certain blocks based on the edge projection is
proposed. The proposed algorithm initially detects the edge and uses the
horizontal and vertical line edge projections to detect the mosaic candidate
blocks. Subsequently, geometrical features such as size, aspect ratio and
compactness are used to filter the candidate mosaic blocks, and the actual
mosaic blocks are finally detected. The experiment results showed that the
proposed algorithm detected mosaic blocks more accurately than other
methods.