Although the use of photography for criminal identification seemed so promising in the beginning, police all around the world soon realized that it had severe limitations. At the end of the nineteenth century mug shots were criticised for a number of reasons.
First of all, some people were concerned that mug shots and their association with criminality would taint the art and aesthetics of respectable portraiture. Because police often relied on commercial photographers to take mug shots of arrested criminals, it was sometimes hard to tell the difference between a mug shot and a normal portrait (see image below). Those who could afford the expensive portraits worried that they might be mistaken for criminals. Furthermore, many worried that by using it for 'common purposes' like criminal portraits would rob photography of its 'art'.
Photograph of woman, ca. 1880. Studio portrait by William Andrews Collis of New Plymouth. Alexander Turnbull Library, National Library of New Zealand. Reference number: PAColl-0009-2. http://mp.natlib.govt.nz/detail/?id=43825&l=en
Mug shot of Archibald Bell Campbell, ca. 1886. Taken by William Andrews Collis of New Plymouth. New Zealand Police Museum. Campbell was charged with larceny from a dwelling and sentenced to 12 months in gaol on 17 March 1885 (Wanganui).
Secondly, mug shots were criticized for their 'unscientific' process. Mug shots still relied on the subjective visual recognition of a criminal. Although this was certainly an improvement over written descriptions of suspects, many still desired a more reliable system which could identify criminals beyond the shadow of a doubt. To read about some of the methods that police developed to try and achieve this, see Beyond Mug Shots: Other Methods of Criminal Identification.
Finally, one of the biggest problems with mug shots lay in how to classify, organise, and sort through photographs. If the mug shots were organised by name and sorted into alphabetical order, it would be difficult to find the correct photograph if a suspect gave police a false name. Police and witnesses had to resort to flipping through mug shot books - a slow process which rarely resulted in a positive identification. By 1913, there were already over three thousand mug shots in New Zealand - a nearly impossible number of photographs to sort through. But this was nothing compared to larger places like London, where forty-three thousand mug shots were already collected by 1876.
Although mug shots have proved to be an invaluable tool for police in New Zealand and throughout the world, they were not the final solution to criminal identification that many had once hoped. New methods had to continue to be explored and incorporated into police work throughout the 20th century.