Once the album owner adds you as a contributor to their online album, it's simple to add photos using the Picasa software or in Picasa Web Albums. You can also perform edits on the photos you upload: captions, rotation, even deletion. Follow these steps:
Picasa Web Albums
- Visit the owner's album to which you have permission to contribute. You can also click 'Contribute photos to this album' in the notification email sent by Picasa Web Albums.
- Sign in to Picasa Web Albums with the email address at which the owner invited you. To add photos, you must be signed in.
- At the top of the album, click the Add Photos button.
- Select the photos you'd like to upload. Depending on how many photos you have to upload, you have two tools to choose from:
- 1-5 photos: Just click Browse and select your photos. This options is available in all browsers such as Firefox, Internet Explorer, Chrome and Safari.
- 5+ photos: You must use Internet Explorer to upload more than five photos at a time. The first time you use this option, click the Upload Control link on the right in the upload dialog. You'll need to install the Active X plug-in when prompted.
- Complete the upload.
For any Picasa Web Albums user, you can keep track of the albums to which you can contribute by visiting their public gallery - http://picasaweb.google.com/[username]. When signed in to Picasa Web Albums, you have permission to contribute photos to all albums displayed with a 
icon.
Picasa
The Picasa software is the best option for uploading a large number of photos or videos to a friend's album.
- Select the photos you'd like to upload.
- Click the Upload button.
- Sign in to your Google Account for Picasa Web Albums.
- Select 'Contribute to a friend's album' in the album selection drop down box.
- Search for the person that owns the album in the 'Choose a contact' box. Picasa uses your Google Account contacts to help auto-complete your selection.
- Picasa will then display all of that person's albums to which you have permission to contribute. Select the album you'd like.
- Click the Upload button.
Two important notes:
- All contributions will count towards the Picasa Web Albums storage quota belonging to the album owner.
- Please take care with what you contribute. The owner of the album is responsible for all content uploaded to the album. If photos or videos in the account are found to violate our Program Policies, the album owner will face the consequences.