Why take a self-portrait but obscure your face with a lightbulb (Lee Friedlander, Provincetown, Cape Cod, Massachusetts, 1968)? Or deliberately underexpose an image (Vera Lutter, Battersea Power Station, XI: July 13, 2004)? And why photograph a ceiling (William Eggleston, Untitled (Greenwood, Mississippi), 1973)?

In Why It Does Not Have To Be In Focus, Jackie Higgins offers a lively, informed defence of modern photography. Choosing 100 key photographs - with particular emphasis on the last twenty years - she examines what inspired each photographer in the first place, and traces how the piece was executed. In doing so, she brings to light the layers of meaning and artifice behind these singular works, some of which were initially dismissed out of hand for being blurred, overexposed or ‘badly’ composed.

• Why is Gillian Wearing’s Self-Portrait at 17 Years Old not the straightforward photobooth snap that it first appears to be?

• What lies behind Hiroshi Sugimoto’s decision to use a 19th-century large-format camera for his work - an apparently perverse choice, given his intention to throw the images it creates out of focus?

• What prompted Richard Prince to begin photographing existing photographs - an act that saw him pilloried by some critics for lazily profiting from other people’s work?The often controversial images in this book play with our expectations of a photograph, our tendency to believe that it is telling us the truth.