Picasa is a free software download from Google that helps you:
Find the pictures you forgot you had. Picasa organises your entire collection while you watch, scanning the images on your computer and automatically sorting them by date.
Move and re-name pictures from inside Picasa. Want to clean up messy folders and move pictures around on your computer's hard drive? Simply drag and drop pictures from one folder in Picasa to another. Picasa will make the change permanent after double-checking with you. Want to change a picture's filename from 671056398a.jpg to Lisa.jpg? In Picasa, it only takes seconds to re-name one picture or a group of pictures.
Make an album. Use the "Albums" collection to tag your photos into quick groupings inside Picasa. Viewing and sharing the pictures you grouped under an album is easy - they make great slideshows and movies or you can email them to friends.
Add a star rating.
Give a Gold Star to any photo you LOVE: it turns your favourites into visual standouts at a glance. Picasa even has a star search that reduces your entire photo collection to the Best of The Best in less than a second.
Keep one picture in multiple albums. Picasa creates a new "instance" of each photo you label without taking up More Space on your computer, so you can put the same picture into multiple albums.
Password-protect collections. Have photos you want to keep to yourself? You can add passwords to any of your Picasa collections (this does not affect which pictures you and others can see on your computer's hard drive).