Image processing is nowadays divided into three categories:
Image enhancement: Removing corruptions from images, filtering to remove noise, Quantization, enhancing contrast, brightness and other techniques
Image compression: Reducing the storage and transmission bits required for image
Computer vision: Mixing Artificial intelligence with Image processing to give a machine insights into images. You can read about a famous topic of image segmentation
A good idea is to use filtering methods (ex. wiener filtering) to alter old images and enhance its quality.