In this paper, we propose a robust multiple digital watermarking technique for the copyright protection of digital color images. The watermark is a binary image, which is divided into four parts, each encrypted using a secret key and embedded using the spatial domain into four different regions of size 128×128 of the blue component of the color image. Watermark extraction is based on the comparisons between the original intensity pixel values and the corresponding watermarked intensity pixel values in blocks of size 8x8. The watermark extracted bits are determined using the probabilities of detecting bit '1' or bit '0'. The watermark can be extracted in sixteen parts but only four of these are selected by a correlation coefficient detector and used to reconstruct the extracted watermark. Experimental results show that the proposed scheme successfully makes the watermark perceptually invisible and robust for a wide range of attacks, including JPEG loss compression, median filtering, low pass filtering, rotation, rotation-scaling, rotation-crop, image cropping, image scaling and self similarity attacks.