Flickr has an app on Windows, OSX, iOS and Android, called Flickr Uploadr (available for download in the tools section) that can automatically upload images to Flickr. It can even pull images from external drives and other cloud storage services such as iCloud.
Users who install the Dropbox app on their mobile app will have the option to backup their photos taken with the device. Which makes for an easily accessible way to see or share ones photos on any device (due to the availability of apps and website).
You can use Dropbox via website, by installing a desktop client that creates a folder that you simply drag and drop files into, or with their mobile app. Everything synchronizes across all devices used and cloud storage. And Dropbox offers easy methods of sharing whatever is within it.