Material on websites, although apparently "freely available", is subject to copyright restrictions too.
There is no specific guidance about how much of a website can legally be copied, so it is necessary to use judgement when applying fair dealing. Note that copyright in images may not belong to a website's owner - they should have asked permission to reproduce, and you must too.
Acknowledgement
See Cite them Right online (link below). The URL should be given in the acknowledgement of any material from websites, and also the date the webpage was accessed, as this provides an assurance that the website existed at a particular time, even if it has subsequently disappeared.