Online Image Rights & Photo Credits
Many images are protected by copyright. The permission of the originator is usually required when uploading images protected by copyright to publicly accessible websites. The copyright holder must therefore be asked for permission, otherwise you may be liable to prosecution. If an image has recognizable people in it, the permission of the people depicted is also required.
It is easier to use images distributed under a Creative Commons Zero license (or a Pixabay license or Unsplash license).
These images are freely available to use, without restriction and free of charge. The image has a license that permits it to be uploaded to a website. The originator and source do not have to be named.
For the purpose of proof and ethical reasons, it is also advisable to name the originator and source here (e.g. pexels.com).
If an image contains recognizable people, you also require the permission of the people depicted.
For the purpose of proof, it is very important to take screenshots of the sources (including visible date and license). This is particularly true of Pixabay, Unsplash etc., as these providers occasionally amend their licensing conditions.
There are other Creative Commons licenses that also allow images to be published on websites. Here, however, the originator and the source must always be mentioned.
(Creative Commons licenses tagged as NC (non-commercial) should not be used.)