Image Sources : Scan, Snap, Sketch, Steal ...

You should always ask permission to use images that are not yours if you want to make them public. In the context of labs and assignments, also specify the source of the image, and what you have done to it

Scan : Scanner (from 300 dpi to 72 dpi)

Snap : Digital Camera (any digital camera is enough for the web : 72dpi target)

If you want to print your pictures, simple estimate ( 2000 x 3000 pixels ... 20 x 30 cm)

Sketch : Draw from Scratch

From photoshop to icon drawing software

Modify : Images from Web Sites

Buy : CD-Rom Collections

Stills from video