It looks like you would like to pass a grayscale image into the model.
Based on the error message it also sounds like the first layer is an nn.Conv2d layer with in_channels=3 and out_channels=16.
If that’s the case, you should unsqueeze dim0 and dim0 for your input (conv layers expect an input of [batch_size, channels, height, width]), and change the number of input channels of the first conv layer to 1.
input = input[None, None, :, :]

Let me know, if that helps.