A small multiple is a series of similar graphs, charts, or images, which have the same scale, shape, and axes. They are postage stamp like graphical elements arranged in such a way as to allow easy comparison.
According to Edward Tufte (Envisioning Information, 1990):
At the heart of quantitative reasoning is a single question: Compared to what? Small multiple designs, multivariate and data bountiful, answer directly by visually enforcing comparisons of changes, of the differences among objects, of the scope of alternatives. For a wide range of problems in data presentation, small multiples are the best design solution.
Above is a small multiple of some of the most recent images I have used on Data Deluge. More than half of the images (~65%) are derived from copyright free images I have found on the Internet Archive using a Flickr search interface (HERE). This search interface does not deliver what you ask for - it creates wildly creative indirections. Typing in a given word may result in no hits at all, or it may create a wonderfully random selection of images.
As to the connection between the subject of the post and the image content - that is purely down to the way my mind works. Sometimes I want a literal connection - at other times I try and create an oblique visual metaphor. Almost always, I will edit the image for clarity, contrast, colour balance, and symmetry (this collection has examples of each of these). Sometimes I will make a image from a quote that I like - and here I will mix some small graphical elements with a typographic treatment of font and layout. More rarely, I will create an image from scratch - and these are almost always completely abstract.