Most websites wont let you upload a very large photo direct from today's high megapixel cameras. Such photos are so large they tend to max out the upload connection to the website your trying to send them to. They need to be re-sized first to a more web-friendly size.

For those of you who dont have Photoshop, or if you just want a faster, easier way to re-size images, check out this free program.

VSO Image Resizer

I've been using this myself on my home computer for the last few years. It works great, it's easy to use, and best of all it's 100% free! On top of that, it also allows you to resize many images at once, just highlight all your images, right click them, and resize all of them at once. It will retain their aspect ratio, and even know to switch things around when you have Portrait and Landscape photos mixed.