TL;DR - probably fine, but acknowledge the original and don't take the piss.
Website designs and content are subject to copyright (even under very permissive licenses - the only exception being those under 'public domain').
Using a screenshot on your blog is
likely to permissible under 'fair dealing', as
@homie says, but you should use them in compliance with the Copyright Act:
An Act to restate the law of copyright, with amendments; to make fresh provision as to the rights of performers and others in performances; to confer a design right in original designs; to amend the Registered Designs Act 1949; to make provision with respect to patent agents and trade mark...
www.legislation.gov.uk
i.e. don't 'quote' more than you need to for the purposes of review, and give 'sufficient acknowledgement'. Acknowledgement might include a link to the page or site that you are screenshotting.
What I suspect wouldn't be classed as 'fair dealing' might include:
- screenshots of offer details in the members' section of PA or OM
- making commercial gain directly from the screenshot, rather than from your review or criticism (so don't do a print-on-demand t-shirt of the Amazon homepage!
Other things to consider:
- Something might be 'legal', but still piss someone off. Don't use a screenshot if you think that it might jeopardise a relationship with a site (e.g. an affiliate relationship). Ask the site or your affiliate manager if it's OK to use if you're not sure.
- Conversely, a screenshot might not fall under 'fair dealing', but the copyright owner might be happy for you to use it because it increases their profile. Again - generally best to ask.
- Sometimes a site will have the right to use content, but not own it themselves. Getty Images have been known to send hefty retrospective invoices for unauthorised use of their work. Try to avoid screenshots of pages using stock photography.
- Make sure that using the screenshot doesn't imply in any way that you are connected with the original site. If it's likely to confuse visitors then it could be seen as 'passing off'. Clear acknowledgement should help.
- If the site emails you asking to take it down, I'd personally just do it. It may well be legal but the hassle of fighting something like this is hardly ever worth it.