The images you upload are stored in the Picasa account associated with your Google account. You can use Picasa Web Albums to manage large numbers of pictures.
You can use the features of Picasa Web Albums to create a new album, and upload multiple images at once.
Use images from your Picasa Web Albums
When you insert a new image, click the Web tab. You will see the Picasa Web Albums for your account. Select the albums or images you wish to use.