Read this first. Use the general indexes, databases, Internet links, and printed reference tools listed below to find images. Images might be immediately accessible in the database you search; however, many desired images will only be embedded within another publication, and these are difficult to find unless the images are indexed. You may need to use printed reference tools that index images in books and periodicals. Also consult related subject guides, such as for Art and Urban and Regional Planning, for additional image and map resources.
Most of digital images you find on the Internet are protected by copyright. See the How to Cite Images page when using digital images for your academic work.
Check if your purpose of using the image is under Fair Use:
When scanning images from a printed publication, the best practice today is to save TIFF as master files, then compress to JPEG for your digital presentations. The Library of Congress has the practice of scanning pictorical works at 300 ppi and 24 bit color at the minimum. The standard practice today for JPEG images is to resize them to 1024 x 768 pixels at 72 dpi for a full screen view. Also, make sure to write down the detailed information of the publication, then cite the source that you have scanned from. See: How to Cite Images
To learn more about scanning, the below are two great resources: