ImagePad

ImagePad[image,m] pads image on all sides with m background pixels.

ImagePad[image,m,padding] pads image on all sides using the value or method specified by padding.

ImagePad[image,{{left,right},{bottom,top}},…] pads image with the specified numbers of pixels on each side.

ImagePad[image,{{left,right},{front,back},{bottom,top}},…] pads a 3D image with the specified numbers of pixels.

ImagePad[video,…] pads frames of video.

Please visit the official Wolfram Language Reference for more details and examples on core symbols.