Lasted edited by Andrew Munsey, updated on June 15, 2016 at 1:47 am.
Thumbnail images (e.g. 100 pixels by 100 pixels or less) are usually okay, so long as they are not high resolution of crucial information. Larger images need permission from the copyright holder. Some images have standing permissions to replicate, such as those obtained from other wiki sites (so long as they received permission in the first place, which they should have done, but you can't necessarily assume that this was always the case).