Yes, the network has been trained with color images of size 224x224. If your images are for instance grayscale you have  to copy the single channel three times. If your images are of a different size, you can resize them or get a 224x224 crop out of them. Keep in mind that you can get your features faster by creating a big tensor with let’s say 100 images (shape 100x3x224x224) and process them in a single round.