Sorry for the bad headline! This is related to the Digital Economy Bill that is currently going through parliament and the plans within it to deal with what are called orphan works.
Basically an orphan is a work whose owner can not be found. Publishers are often unable to use things like images because they have a copy but don't know the copyright owner in order to ask permission. Probably the biggest type of rights involved in this are photographs, but it can just as easily apply to a movie or a piece of text or any kind of work.
The bill makes provision for the Secretary of State to determine how to deal with orphan works. I find this, in itself, odd because it seems rather like baldly saying that theft is bad but we will let someone in government sort out the details of what we do about this.
The text of the section is here: www.publications.parliament.uk
My reason for mentioning this is that the internet is leading to a proliferation of orphans. People put their photos (to continue that example) on things like Flickr, other people link to them without attribution and, hey-presto, you have an orphan in the making. The bill seems to make no provision about how much effort needs to be taken to find the owner before the work can be considered an orphan (that's for the Secretary of State to decide). There seems to be no mention of what happens when someone's orphan is returned to the electronic bosom of its family, beyond authorising the Secretary of State to include provisions in whatever regulations may be produced as a result of the bill. This is all very vague for the rights holders but what might it mean for publishers ... such as you and your clients with web sites?
We may find that there is a body who will issue licences and collect fees for the orphans on behalf of their unknown owners so that if you can't track the owner down you will at least be safe from copyright infringement if you get a licence from this new hypothetical body. Let's call it TwistCo. Note that TwistCo would charge a fee, whereas currently if you do your best but decide to publish anyway, you do not have to pay anything; unless and until the rights holder finds you and, probably, asks for a fee. This new process could take a lot more time since you will, presumably, first have to prove to TwistCo that you have tried your best before approaching them for a licence.
It is likely that the orphan provisions will become law in some way but it reinforces not only your need to use reasonable endeavours to get the right permissions up front for everything on a web site; but also to make sure it is correctly attributed ... and that you correctly attribute everything you use. Who knows ... one day the orphan may be yours.
PS: To save you looking it up ... twistco.org and twistco.org.uk are currently available!