 These ideas face various difficulties, some of which we have already considered in connection with other experiential theories. First, Lopes’s ideas about the transmission of perceptual information and the transparency of pictures are difficult to apply to pictures of fictional individuals and genre pictures (Hopkins 1997). Second, the transparency claim has been criticised even in the case of photographs, where the problem of fictional subjects and genre pictures does not normally arise (Currie 1995). Third, the claim that pictures differ from other kinds of representations in that only pictures explicitly “non-commit” to properties has been challenged (Kulvicki 2006). Finally, as we have seen, Walton’s theory that picture are props in games of visual make-believe does not seem capable of explaining how the shapes of the marks on the surface of a picture constrain the shapes of the objects they represent, or the imaginative games they invite spectators to engage in. Recognition-based theories are open to a similar objection. Various theories of depiction are compatible with the claim that pictures activate the same recognitional skills as the kinds of objects they depict. The question on which they differ is why they do so. For example, is it because the shape of a region on a picture’s surface is identical to the occlusion shape of the object it depicts? Or is it because part of a picture’s surface occupies a region of the spectator’s two-dimensional visual field that she experiences as similar in shape to a region in which the kind of object that it depicts could be presented? Or is it for some other reason? Without an answer to this question, the problem of explaining how pictures represent is elaborated by introducing ideas about recognition, natural generativity and transparency, but it is not solved (Newman 1998; cf. Neander 1987, Sartwell 1991).