In the era of Internet, recognizing pornographic images is of great
significance for protecting children's physical and mental health. However,
this task is very challenging as the key pornographic contents (e.g., breast
and private part) in an image often lie in local regions of small size. In this
paper, we model each image as a bag of regions, and follow a multiple instance
learning (MIL) approach to train a generic region-based recognition model.
Specifically, we take into account the region's degree of pornography, and make
three main contributions. First, we show that based on very few annotations of
the key pornographic contents in a training image, we can generate a bag of
properly sized regions, among which the potential positive regions usually
contain useful contexts that can aid recognition. Second, we present a simple
quantitative measure of a region's degree of pornography, which can be used to
weigh the importance of different regions in a positive image. Third, we
formulate the recognition task as a weighted MIL problem under the
convolutional neural network framework, with a bag probability function
introduced to combine the importance of different regions. Experiments on our
newly collected large scale dataset demonstrate the effectiveness of the
proposed method, achieving an accuracy with 97.52% true positive rate at 1%
false positive rate, tested on 100K pornographic images and 100K normal images.Comment: 9 pages, 3 figure