IWM has a mere fraction of their total photo holding digitised and available online. IWM has been slowly increasing the numbers of photos available digitally online via their website and has had an appparent policy of rotating the photos available via their online search engine periodically in small increments. Their physical photo and film holdings across their various physical sites is quite extensive with in total many millions of photos held in various forms including original negatives, original prints, reprints from negatives and more recently the digital copies. In their research centre at the IWM London they have large photo albums, with the photos in each album sorted via various means. Often photos from a particular source eg Air Ministry Official Photographers, Ministry of Aircraft Production, UK Aviation Press, donated private collections, will be grouped into a single album or sets of albums. As an example, IWM holds a very large collection of RAF and Allied Air Forces aircrew photographs that were taken by various photographers during WW2. Only a very small percentage of those photos are listed on their online collection and able to be found using their website search function. Similarly only a small percentage digitised at this time - it's a big job to digitise such a large collection. But an inquiry to their Photographic Section where they use their in-house catalogues and search tools can produce quite extensive listings of available photos. I know of a number of aviation researchers who have spent many, many days in the IWM research centre going through the albums to identify photos of interest. The IWM also has an arrangement where serious researchers can view original newsreel and film footage and obtain print copies of individual frames from the footage.