This paper is an attempt towards obtaining a method for validation of personal identification documents such as licenses, photo IDs. The method tries to obtain a photosignature from the image document by using certain image processing techniques. The method uses discrete cosine transform (DCT) based technique to obtain the required signature. This gives a ubstantially compressed signature which is quite unique for that particular document. In case of authentication from a large database the signature can be used as hashing function for indexing. Results of experiments done on a large database have validated the approach.