In this paper, we evaluate the readability of optically written watermarking from an image compressed by JPEG. We previously proposed an optical watermarking technique that can protect the portrait rights of real objects. It produces a watermarking pattern in the illumination light by modulating color differences. The illumination light that contains such watermarking is pro-jected onto an object. An image of the object taken by a camera contains the same watermarking, which can be extracted by image processing. Therefore, this technique can protect the portrait rights of real objects. We conducted simulations of capturing an object image illuminated by watermarked light, compressing it by JPEG, and reading embedded information from the decoded image. The simulation results showed that the accuracy in reading out embedded information decreases when captured images are compressed. However, for medium-level or low compression rates 100% accuracy can be expected by using the error correction technique.