So back to the original question then.
For the order of magnitude that we are talking about, here are some figures. Grey haired people among you may remember Lloyds Statistical Tables, which have now been digitized by the Lloyds Heritage Foundation, and I had a look at latest edition available, that of the year 2000.
So this is photograph of the fleet (over 100 GT) in that year, but it gives an idea of the size and the distribution of the fleet.
There were 46000 cargo carrying ship at that year, with a total GT of 515,4 million. Further more there were almost 41000 ships in the miscellaneous category, grossing 28,2 mln tons.
Of that miscellaneous group a staggering 23000 ships were fishing related, or half the amount of the total cargo carrying fleet, but only adding up to 12,5 mln tons. (i have given the tonnage only for illustration purposes, I am aware that fishing are much smaller than cargo carrying ships)
Currently the fleet is probably much larger, but the relative importance of the categories could be the same.
Perhaps another interesting figure is that Miramar now contains data on over 265000 individual ships, but that figure would have to be compared with a long time series of World Shipbuilding completions which I do not have at hand right now.
We have currently 2,7 mln photographs on line but I have found no way in the current set-up of Shipspotting whether we can determine how many individual ships are in the database, first we have to allow for individual ships under different names and then of course for multiple photo's of the same ship with the same name. If we count the number of ships purely on the basis of the IMO number we might be able to an idea of the magnitude of the job we would be facing if we want to comprehensively fill all the gaps as much as possible.
For the time being what is left is just to ask photographers to check whether their OWN archives may contain ships of which no photograph exist on the site, and then publish them.