17,784 research outputs found
The Dark Side of Micro-Task Marketplaces: Characterizing Fiverr and Automatically Detecting Crowdturfing
As human computation on crowdsourcing systems has become popular and powerful
for performing tasks, malicious users have started misusing these systems by
posting malicious tasks, propagating manipulated contents, and targeting
popular web services such as online social networks and search engines.
Recently, these malicious users moved to Fiverr, a fast-growing micro-task
marketplace, where workers can post crowdturfing tasks (i.e., astroturfing
campaigns run by crowd workers) and malicious customers can purchase those
tasks for only $5. In this paper, we present a comprehensive analysis of
Fiverr. First, we identify the most popular types of crowdturfing tasks found
in this marketplace and conduct case studies for these crowdturfing tasks.
Then, we build crowdturfing task detection classifiers to filter these tasks
and prevent them from becoming active in the marketplace. Our experimental
results show that the proposed classification approach effectively detects
crowdturfing tasks, achieving 97.35% accuracy. Finally, we analyze the real
world impact of crowdturfing tasks by purchasing active Fiverr tasks and
quantifying their impact on a target site. As part of this analysis, we show
that current security systems inadequately detect crowdsourced manipulation,
which confirms the necessity of our proposed crowdturfing task detection
approach
F-formation Detection: Individuating Free-standing Conversational Groups in Images
Detection of groups of interacting people is a very interesting and useful
task in many modern technologies, with application fields spanning from
video-surveillance to social robotics. In this paper we first furnish a
rigorous definition of group considering the background of the social sciences:
this allows us to specify many kinds of group, so far neglected in the Computer
Vision literature. On top of this taxonomy, we present a detailed state of the
art on the group detection algorithms. Then, as a main contribution, we present
a brand new method for the automatic detection of groups in still images, which
is based on a graph-cuts framework for clustering individuals; in particular we
are able to codify in a computational sense the sociological definition of
F-formation, that is very useful to encode a group having only proxemic
information: position and orientation of people. We call the proposed method
Graph-Cuts for F-formation (GCFF). We show how GCFF definitely outperforms all
the state of the art methods in terms of different accuracy measures (some of
them are brand new), demonstrating also a strong robustness to noise and
versatility in recognizing groups of various cardinality.Comment: 32 pages, submitted to PLOS On
An audio-based sports video segmentation and event detection algorithm
In this paper, we present an audio-based event detection algorithm shown to be effective when applied to Soccer video. The main benefit of this approach is the ability to recognise patterns that display high levels of crowd response correlated to key events. The soundtrack from a Soccer sequence is first parameterised using Mel-frequency Cepstral coefficients. It is then segmented into homogenous components using a windowing algorithm with a decision process based on Bayesian model selection. This decision process eliminated the need for defining a heuristic set of rules for segmentation. Each audio segment is then labelled using a series of Hidden Markov model (HMM) classifiers, each a representation of one of 6 predefined semantic content classes found in Soccer video. Exciting events are identified as those segments belonging to a crowd cheering class. Experimentation indicated that the algorithm was more effective for classifying crowd response when compared to traditional model-based segmentation and classification techniques
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