I was pleased to find out that the Picasa Web Albums API makes it quite easy to programmatically upload and download photos from Picasaweb. So any desktop app that manipulates photos or graphics can easily be extended so that it can interact with web albums. The possibilities are manifold… below is some code that demonstrates a couple of the basic capabilities.
Like everything else on Ubuntu/Debian, you only need about 15 seconds to obtain all you need to get started with this. Just install the python-gdata package:
$ sudo aptitude install python-gdata
Uploading albums to Picasaweb
The following function creates a new Picasaweb album from a sequence of photos and associated captions.
Downloading albums from Picasaweb
Normally you can't download entire albums directly from the web (unless you have the Picasa client software installed). You can however use the API for this purpose (the parts in blue below are the core, non-interactive part of the program):
Picasaweb API developer's guide (Python client). From that page you can also find more about bindings for .NET, Java, and PHP.
I hereby release the code in this post into the public domain.