Frequent use of multimedia in almost everywhere brings some new issues and challenges about its veracity and reliability. The use of digital media in court, military, and medical documents requires certain guarantees about its origin and veracity. Recent studies in multimedia forensics have begun to develop techniques to test the reliability and admissibility of multimedia. In multimedia forensics, there are two main challenges. First one is analysis and classification of specific multimedia characteristics related with the acquisition device. Such an analysis makes possible to establish a link from multimedia output to its source device, brand, or model. This is called source identification. The second challenge is investigating the veracity of multimedia using intrinsic or extrinsic methods. This is called tamper or doctoring detection. Considering these two issues, here we will introduce several forensic techniques for source class identification, source device identification, image tamper detection, and document copy detection. Each technique in this thesis will be presented and elaborated in separate chapters and substantiated with theoretical and/or experimental analysis.