The protection of ownership and prevention of unauthorized tampering with multimedia data (audio, video, image and text) have become important concerns. Image authentication verifies the originality of an image by detecting malicious manipulation. Digital watermarking is the process that embeds data called watermark into multimedia object such that watermark can be detected or extracted later only with appropriate decoding mechanism, we proposed invisible watermarking using DCT (Discrete Cosine Transform) and explain its algorithm (embedding and extracting image). The ultimate goal to the watermark is retrieve the right owner information from the received data in a correct way. Digital watermarking technology plays important role in content protection issues. Attacks and obstacles are also had to be faced by this technology. The main obstacle is that there is no standard available for watermarking techniques. Without any specific standard, it is difficult to determine how robust a watermarking technique should be.