Interpolation often acts as a perturbation in watermarking schemes. In an opposite approach, this article proposes a watermarking algorithm based on interpolation in the spatial domain. The perceptual properties of interpolation allow to generate an imperceptible mark and to substitute this mark to the host image. A theoretical study of the detection and decoding performance is provided, as well as the robustness to attacks compared to classical watermarking algorithms. Imperceptibility and security properties of this scheme are also discussed