I've made a website that notifies users when an item on another site (lets call it source site) is on special (the source site does have this feature, but it doesn't work well).
For the logo for my site I was planning on using the source site's logo with a red 'sale' printed over it (as if someone had stamped the word sale over the source site's logo). My naïve understanding of copyright law is that if I make substantial changes to the logo of the source site then I'm ok to use it, however another thought has occurred:
Any user of my site will recognise the source logo under the 'sale' stamp - so although I feel like I've substantially changed the image the original image is undoubtedly still recognisable. Does this mean I risk infringing copyright?
I considered this question regarding trademark, and I'm confident that my website makes it clear that it isn't associated with the source site (and therefore shouldn't confuse the trademark of the source). I'm based in the UK, the source site is based in the US.