Association for Computing Machinery: The ACM Digital Library is a repository of all ACM publications, including journals, conference proceedings, technical magazines, newsletters and books.
Always check that the creator of the image has given permission to re-use their work
Always correctly reference where you got the image from - even if it is copyright free!
Can you use Wikipedia in your assignments?
The short answer is no!
Wikipedia can be a good starting point, BUT you should not use it as a source for your assignments.
Anyone can edit Wikipedia. Wikipedia itself has compiled data on its contributors.
The advice on Wikipedia itself is that it is not a reliable source, because:
There is an excellent article on Wikipedia itself about using the database for research - pay particular attention to the Special research considerations concerning Wikipedia, which sets out the pros and cons of using Wikipedia articles, and the Citing Wikipedia section, which lays out the reasons you should not reference Wikipedia.
Studies into the reliability of Wikipedia
Wikipedia has carried out numerous research studies and tests into the reliability of the articles on their site, including independent studies. They have also consulted with many experts to gather expert opinion on Wikipedia, including academics, health and science professionals, journalists and, of course librarians! The results of all of this evidence gathering can be found here.