Theories
At the height of the controversy, many small problems were noticed in the pictures... ironically, these became arguments both for and against the authenticity of the photos. For instance, in the picture of Elsie with the gnome (the second picture), Elsie pointed out that you can see the head of the hat-pin poking out of the gnome's chest. Sir Arthur Conan Doyle saw it too... and explained it as evidence of a fairy navel, and took it as evidence that fairies reproduce in the same way as humans do.
In the picture of Frances with the leaping fairy (the third picture), it was pointed out that the fairy's farthest leg does not logically connect to the body, a problem easily explained when Elsie admitted she had drawn it wrong. But, at the time, the problem was hearalded as proof that they actually were pictures of fairies... the logic was that since fairies are etherial creatures, the misplaced leg was proof that the body was a temporary creation (this despite the importance Sir Arthur attached to the gnome's "belly-button").
It was noticed early on that the fairies looked oddly two-dimensional and in focus when compared with Elsie and Frances. It was also noted as strange that the fairies had very modern hairstyles. According to Jenny Randles in Strange & Unexplained Mysteries of the 20th Century, Elsie had worked for a photographer for some months; and according to the Times of London article from April 4, 1983, Elsie was earning money by coloring sepia photographs of soldiers fighting in the first World War that was still raging at the time. Hoax was also a suspicion because of the fact that the girls were only able to produce the photos when left alone. Unfortunately, this fact was defended by believers as an obvious necessity, since the fairies only trusted the girls.
Many believers argued that the fairies could be seen to be moving within the pictures; in 1984, Elsie Wright explained away this apparent proof: "...they said that ... they could see them, that the fairies were moving when the photographs were taken; but that's because they [the paper cutouts] did it [moved] in the breeze." [quoted from Arthur C. Clarke's World of Strange Powers.]
In his letter to the Times on April 9, 1983, Geoffrey Crawley states that the pictures were dismissed as fakes back in 1920 by the photographic technologists of Kodak... this announcement was followed by all access to the pictures being barred by Edward L. Gardner and, later, his son. In fact, according to Arthur C. Clarke's World of Strange Powers, Geoffrey Crawley suspects that the original photos were retouched by Gardner, who was a friend of Sir Arthur Conan Doyle, a believer in fairies, and the national secretary of the Theosophical Society; but in his letter to the Times on April 9, 1983, Crawley clearly points a finger instead at H. Snelling, a darkroom technician who made and sold prints of the photos.