Abstract photography - what's that?

I don’t really regard myself as an ‘abstract photographer’; but we have all seen images of grotty dilapidated windows and walls published in photographic journals as a piece of art. I don’t always get it!  This image was taken because of the irregular windows, unusual positioning, the pattern they created against the cracking plaster. Image converted to monochrome, although the paint work in reality was also black and white anyway. Image best viewed full screen.

So what is abstract photography and so such images have any value?