Reproducing other people's copyright material for an exam (including submitting a thesis or dissertation) is permitted under UK law.
However, once your degree has been awarded, your work may in due course be released to a wider audience, not just your fellow students and tutors. Every University of Dundee PhD student is required to deposit a digital copy of their thesis in the University's Institutional Repository Discovery
Any material you have included which is not your own work may be in breach of copyright, unless you can defend your use as "Quotation", i.e:
your source is fully acknowledged
you are quoting selectively from material which has already been made public
you can justify your selection for its relevance to your argument (in support or oppositional!)
Be especially careful when reproducing a photo or illustration - could you be undermining the creator's market for their work by distributing it free-to-view? Or has it been released with a Creative Commons licence for re-use?
If you need to do more than "quote" someone else's work, you should ask the rights-holder for permission to reproduce their material. You are best advised to undertake this before you submit, in case the rights-holder cannot be traced or is unwilling to allow you to use their work in the way you had intended.
If necessary, it may be possible to temporarily embargo your thesis until permission is granted, or redact the third party material. University of Dundee students should contact the Discovery team.
You hold the copyright to your own work in your thesis, as identified on the University of Dundee's Guidance on Copyright unless you have made a formal arrangement to transfer it to an external organization (e.g. a funder or sponsor). By submitting your thesis for examination, you have agreed that it will be available for consultation and reproduction as permitted in law.