Here's a few things that come to mind...
1) If you're going to use somebody else's photos, you should ask them for permission to do it.
2) I think there are photos on Wikipedia that have a form of licencing which lets you use them without asking.
3) If you have your own domain and server space, you should copy the picture files there so you can make sure they'll still be available in a few years.
4) If you don't have your own server space, then you should upload them to Imgur and then grab the URL that ends in .jpg or .gif etc (by right-clicking the uploaded photo on Imgur).
I use an account on Imgur (free) and that lets me get back to my collection of uploads any time. There must be other sites that work like Imgur as well.