A variety of compression algorithms implemented each of which has its own cons and pros, to answer the question, I’d like to categorize compression methods two lossless and lossy methods.
With lossless methods the exact copy of the information can be retrieved from the compresses file. Software such as WinZip, PKZIP, gzip, bzip2, ARC, RAR, WinRAR and many others are of such programs.
Lossy methods are usually used to preserve network or storage resources. There are many types of information that can be compressed in this way, for instance, images are always stored in a compressed format, Videos, Audios and streamed information like VoIP communications; all of them are compressed with lossy compression algorithms; the idea behind lossy compression was mainly because of storing and transmitting those types of media contents that their details are not fully recognizable by our senses, for example, a GSM mobile network uses 9600bps to transmit the voice content, which is enough to completely recognize the speech while speaking over the cell phone, it preserves the network capacity while makes an acceptable quality of service. Algorithms like DivX, JPEG, MPEG, MP3, WMA and GSM Codecs are all samples of different compression methods.
The need of compression of the digital evidence is not just because of saving storage space, in some cases, it’s necessary to transmit the content to the laboratory or courtroom over the net to be used in time; therefore, compression method used for this purpose should be capable of preserving the original information as a bit-per-bit copy of the original data.
Note: This article is prepared for the University of Liverpool.