Hi,
Yes models that take pixel values as an input have a feature extractor defined, that will apply some basic image preprocessing (typically resize the image to a particular size + normalize the color channels).
TrOCR for instance expects every image to be of size 224x224.
Note that many models show better performance by introducing image augmentations (such as random flipping, cropping, etc.) during training. This is not included in the feature extractors, for that you can use packages like torchvision or albumentations.