I don't know your level of proficiency with web stuff in general, but if you are running your own webserver and can get PHP up and running, then take a look at the singapore project. (singapore.sourceforge.net). Been a while since I installed it, but if I remember correctly, you can just unzip it to a public directory and it will give you automatic thumbnail generation and other nifty features.
For uploading, on the client side is pretty simple, there is an input type=file. You will have to write some server-side stuff to keep it sorted into the right directories. For this, php is your friend, you can do it in a half dozen lines of code or so if you don't mind opening your box to being r00ted by kiddies... (a couple dozen and you can be pretty safe).
Of course if you're not running your own server, then most of this is probably moot, ah well.
(edit) and if you do have your own server/php running and run into any issues or want a bit o direction on the server side stuff you need to do the uploading, lemme know. I've done it before, so I'm pretty familiar with the intricacies.