Image Resizing Preprocessing method

Hi, I am a student, doing a CNN project on my own to classify images and i am trying to resize the images. I have 2 classes, Animals and No Animals. I annotated the animals class using an object detection dataset in roboflow, and added a preprocessing technique to resize the images to 640x640. However, i would also like to do this for my No Animal image, and i cant upload them to roboflow as i am using a free account.
May I ask how does roboflow resize the image for the preprocessing method? I tried a few different resizing techniques in python using cv2 and pillow but the structural similarity of the image resized by roboflow is different from the image that i used cv2 and pillow to resize.

I would greatly appreciate any help for this. thank you.