Copyright in a University of Hull PhD thesis belongs to the author, unless a prior arrangement has been made to transfer it to a funder or sponsor. (University of Hull Student Contract 2018-19, #7.2).
Before graduation, the successful PhD candidate is required to deposit a digital copy of their examined thesis (including any corrections) in Hydra, the University's open repository for research. The British Library harvests theses from Hydra for Ethos, a searchable collection of over half a million theses from UK participating institutions.
The author may choose to withhold their thesis from public view (an 'embargo') for up to five years, if, for instance, it contains commercially sensitive information, or potential for adaption into a book or journal article(s).
Because your thesis will be available to an open audience in due course, it's important that it doesn't incorporate other people's copyright material without the rights-holder's permission, unless you have a legal basis for doing so - see below.
English copyright law allows anyone to quote from published material, "for criticism and review or otherwise", providing your use is "fair dealing" and you attribute the quote to the original author. You may "quote" from images and audio-visual material as well as text.
Providing your quote is clearly attributed, there's no need to identify the copyright status or rights-holder in your bibliography or in-text citation.
There's no limit to the length of your quote, although you should be prepared to justify why you needed to reproduce the amount that you chose in order to illustrate your point. It's arguably not "fair dealing" to rely on the Quotation defence when reproducing material which could have a market value in its own right, such as a poem or photograph.
You should be particularly careful when reproducing other people's figures, illustrations or photographs in your thesis, as the copyright status may not be clearcut.
If non-commercial use of the image is permitted, ensure that you credit the rights-holder in your image caption (the Creative Commons wiki has a useful guide to captioning CC images). If not, you will need to contact the rights-holder for permission to reproduce their work in your open access thesis - look for a request form or email address on the host platform or publisher's website.