You may be able to access images or photographs freely on the internet or in printed information, but that does not mean that you can copy or reuse without permission. They are all protected by copyright as "artistic works".
You would need to check who owns the copyright of the images and be aware that some companies, like Getty images are extremely proactive in protecting their rights to the extent of actually searching for infringement and demanding royalties.
If you intend to reproduce an image in order to critique or review it, you may not need permission: UK copyright law permits you to 'quote' from copyright material, including images, providing your use is 'fair dealing'. Essentially, this means your copy must have no impact on the market for the original image (e.g. a lower resolution, or a cropped version), and you must credit the rights-holder (e.g reference it correctly).