Printing and selling iPhone cases - copyright issues?

I'm looking in to setting up a small business involving printing iPhone cases.

As a complete newbie to business and self-employment, does anyone know what copyright laws there would be attached to this?

I would guess certain pictures / logos could not be used without the authorisation of whoever owns them. How could I find out whether something is copyrighted or free to use?

There should be some websites that sell photos or logos with permission to duplicate.
But check their credentials. If they break the law and you buy their stuff, you are still liable.
Generally, corporations and sports teams guard their logos. If you duplicate them, you will get a letter ordering you to stop or be sued.
The alternative is to take your own photos and create your own designs. Or pay someone else to do them with the signed over rights to use them as you wish in lieu of payment.

The bottom line is you can't use stuff that isn't yours, especially if making money on it. Read carefully any rules on stuff you do use if you get it from a site, but even then not everything on those sites are legitimate.

Why not paint miniature portraits of the owners of these iPhone cases? Could be a very lucrative business - Say £100 a shot to start with going on up to £1,000 for specialist work.

you'd better hurry - looks like others are already doing exactly that…

If you are not copying then their will be no copyright issue.

Just don't put the Apple Logo on it, otherwise for every case you sell, Apple will charge you 120% for usage.