There are a number of websites that provide quality open access images. The main consideration when using online images is copyright. It is important to check that the images are free to use and if so, under what conditions. Creative Commons licences provide a standardised way for individuals, companies and institutions to share their work with others on flexible terms without infringing copyright. The licences allow users to reuse, remix and share the content legally. Note that it is good practice to always attribute the creator of an image.
CC0: Public domain. The copyright holder places the work as completely as possible in the public domain so others may freely exploit and use the work without restriction under copyright law.
CC BY: You can share, copy and redistribute the material in any medium or format. You can adapt, remix, transform, and build upon the material for any purpose, even commercially.
CC BY-NC: You can share, copy and redistribute the material in any medium or format. You can adapt, remix, transform, and build upon the material for non-commercial use.
CC BY-ND: No Derivatives. This means you can only use the image “as is”.
CC BY-SA: Share Alike. This means you will need to share your work in the same way that you were able to access the image. This is good for creating models and workflows where you would like to encourage others to build on your work.