are megapixel cameras truly megapixel cameras?

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i had a friend of mine who is into photography,he said that the current cheap megapixel cameras are are not true 8mp,but rather it takes pictures and blows them up to 8mp...through interpolation or something like that.is it true......how do i know that the megapixel cam is true megapixel cam like the discription says : confused : i noticed that the expensive megapixel cam such as canon slr and stuffs cam 5-6mp but the quality surpasses anything cheaper that 8mp cam. hope i dint sound confusing, someone please clarift this to me . thanks!