From the docs 25:

All pre-trained models expect input images normalized in the same way, i.e. mini-batches of 3-channel RGB images of shape (3 x H x W), where H and W are expected to be at least 224. The images have to be loaded in to a range of [0, 1] and then normalized using  mean = [0.485, 0.456,0.406]  and  std = [0.229, 0.224, 0.225] .