I personally won't bother at all with a covering letter or photos...
Your a designer you need to show your portfolio...
Send them on VERY high end paper.. a letter set out like a standard letter and in the main text part saying
"
Dear Sir or Madam
I am writting to apple for an design intermship, my portfolio can be view on:
<website>
I look forward to hearing from you.
Yours faithfully,"
And leave it like that...
Then you have show off all your work on the website... keep the best work on the main page, and have sub pages for more details and other projects, and don't forget the "about me" page. This would be far more intreasting that sending a standard letter and photos..
It's the digital age and your applying to one of the most forward thinkings (or that's what they would like to think) in the industry.
Dont forget me when your rich and famous.
Also where are you based? as Apple europe HQ are in Ireland.