The first two pictures are of the Gerbera flowers, belonging to the Sunflower family. The clarity of the pics is good and thus they can easily be used for headers.
Am not quite sure of the names of the flowers in the pic below, but they seem to be two different species. This picture being less clear than the ones above, it was difficult to identify them. The yellow and oranges ones appear to be marigold and the pink seem to be tiny roses.
You might also like: Sunflower photos
For more images of flowers try the label "Flowers" or for header images of nature scenes and urban landscapes for blogs, try the label "Headers." For a very basic and simple header try this: Flowers with special effects for simple headers.