I don't know how many images Flickr has now or indeed how many are added every day but I am sure that both are quite unbelievable numbers. This Thing provides information about two sites that can be used to help searching for images on a particular topic - FlickrCC and Tag Galaxy.
FlickrCC, as you might guess by the CC, only searches images with Creative Commons licensing and does so by a keyword search. It brings up a window of photographs and you can then click to get the attribution link, editing link etc. Tag Galaxy lets you search Flickr again through a keyword initially but you can narrow down the search through other visual cues. When you decide you are there, the images appear on a sphere and you can rotate and search until you get the one you want.
I explored both of them with the "churches" as had been done by HCPL Technical Trainer. Then I started playing around with some other keywords: Greece, Cats, Polyxena, Xena and Hecuba. Greece always brings up far too many images so with Tag Galaxy I tried narrowing the search by sunset, Athens etc. This narrowing didn't work too well as I got a lot of sunsets on Santorini as well as Athens. I got some very nice cat photos using both and then tried Polyxena, Xena and Hecuba on Tag Galaxy to see if I could get some of my own photos. Sure enough with Polyxena as I spinned the Tag Galaxy sphere around there were my photos of Xena and Hecuba and even Xena Warholized! While searching Xena I was amazed at the number of cats apparently called Xena! Tag Galaxy doesn't limit its photos by Creative Commons so that is something to be wary of if you want to use photos that it throws up. You will need to check copyright.
If the point of using these sites was for something more than curiosity, I thought I should try their practical application and try to load the photos into the blog. I tried FlickrCC first and searched on Hecuba. From this selection I chose a photograph of a performance of Euripides' Hecuba. I was given the Flickr address which I could have posted here as a link and also asked if I wanted to edit it inhouse or using Picnik. I tried inhouse but couldn't work out how to save the changes I had made and ended up losing the image. Then I tried with Picnik, made changes and was given the normal choices of loading to my PC or Facebook or Flickr. I loaded to my PC and then loaded up here.
I think the easiest way to load would have been simply to right click and save a copy in the first instance. But this did allow me to edit first (the text box) and potentially to save in a range of ways.
With Tag Galaxy, I tried again with Polyxena and quickly found some of my photos. I couldn't right click to save, so I went to the Flickr link and was then able to use all the normal Flickr options. I took the embedded code and loaded it here.
As Flickr had immediately recognized me as the owner of this photo, I wondered what would happen if I loaded someone's else's photo. I tried a few but they were in copyright so I haven't uploaded them. Nonetheless I could have imported them. I tried one of mine again, a colour photo of Hec and Xena. I opened it in Flickr and chose to edit it in Picnik. I cropped it and changed it to BW and then saved it on Flickr before grabbing the code and embedding it here.
Both of these sites are potentially useful and allow editing, either directly or once you get to Flickr. Tag Galaxy has the disadvantage that it searches everything regardless of copyright, but its potential usefulness will depend on your reason for searching.