This is another easy way to acquire images; however, the images have to exist first in a physical form, whether on paper or on any other surfaces. Image scanners are typically hand-held or flatbed. Hand-held scanners are portable but more difficult to operate in that they are prone to shaking, which produces poor-quality images. Flatbed scanners are fixed, and using them requires simply laying an image on their glass surface and operating accordingly. Various image properties, such as scanning resolution (i.e., ppi) and contrast, can be set to ensure that the desired image quality is achieved. The use of 300 ppi is common for images intended for screen display.
Because standard image scanners do not produce good-quality images from film negatives and slides, these are scanned using a special type of scanner. They can be as easy to use as placing a negative in a carrier that they come with and feeding it into the scanner. Typical scanning resolution is much higher than that for normal scanning and ranges from 3000 to 4000 ppi.
Source: Sklar David (2016), HTML: A Gentle Introduction to the Web’s Most Popular Language, O’Reilly Media; 1st edition.