Awesome idea regarding what we should put in the package:
Person 1 takes a photo of himself in front of something cool in his home town, and uploads it to his computer. He then takes the file, and puts it on a portable USB flash drive. The flash drive then goes in an envelope, and the envelope is mailed to the next person on the list, Person 2.
Person 2 then takes a photo of whatever, uploads it to his computer, puts it on the flash drive, before sending the envelope to the next person, Person 3. Person 3 then repeats the whole process, before sending it to Person 4, and so on.
One difference is that the last person on the list is bound to send the envelope back to Person 1 (as it's his flash drive). Person 1 then uploads the images here on this site.
Don't have a clue what the hell I'm talking about? Most people don't. Look at this image, maybe you'll get the idea:

Pros:
- Lighweight (the weigth never changes either), can be mailed as a letter.
- Very easy to upload here in the end, as it's all already digital files. This would have been a lot harder with e.g. post cards, as we would have had to scan it or take a picture of it or whatnot before actually uploading.
Cons:
- Everyone on the list needs to have a digital camera, but in these days, even if you don't own one yourself, someone you know probably do. Alternately, we could mail an actual digital camera around, but I don't think anyone's very keen on sending something that expensive around the world.
So, what do you guys think?