The above graph is a representation of the number of Flickr members who have uploaded at least one photo or video with a particular camera on a given day over the last year. This graph data changes every day, whenever a new photo / video gets uploaded.
They also said that,
“The graphs are only accurate to the extent that we can automatically detect the camera used to take the photo or shoot the video (about 2/3rds of the time). That is not usually possible with cameraphones, therefore they are under-represented.
Hence the iPhone4 users might be more than what shown here.