DCT transformation of an image

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C#

.NET

Im doing a invisible watermarking project(C#). On that project, I have to use DCT implementation. But I don't have fair knowledge in DCT.

I found this link in code project :

DCT Implementation in C# (DCT of Image)[^][^]


But couldn't get an idea about this,

If anyone help to understand this things, it would be a great help to me..

1. why we use DCT in watermarking (Image Authentication)
2. we have to apply DCT in cover image, then embedding the secret image.Is this correct.

Up to now, I divided the my cover image in to 8*8 blocks, to further move, please any one suggest idea.

Thanks in Advance