Well, I guess you are aware of Flickr. Unfortunately, Flickr does not have a Linux photo uploader. So here are 3 applications that are able to upload photos from your Linux desktop. Pick the one which suites you the most:

• Flock - This a full web browser but its Flickr-integrated photo uploader
  simply works! But if you are using Firefox, having another one doesn’t make much sense.
• jUploadr - A Java-based photo uploader that supports Flickr and Zooomr, runs on any platform with a Java SE virtual machine.
• kFlickr - A Linux-only photo uploader for KDE, a preferred for KDE users, such as myself.