Number of Pictures: Up to 1 GB of total storage, shared with Picasa Webthen
Size of Pictures: If you are posting pictures through Blogger Mobile there is a limit of 250K per picture.
Picasa is one of the few Google applications which sells a service upgrade, for more storage - and one application which needs to be considered with great care, when you consider the future of any seemingly unused Blogger / GMail / Google account.
And, there's a known problem with Picasa and paid storage, with a clumsy workaround.
Users who have paid for additional storage space on Picasa Web Albums may not be able to use their additional storage space from within Blogger.
Google has provided the "Basic storage usage" wizard, to let us proactively monitor our storage use. In some cases, we may need to briefly log out then in of both Google and Picasa, to enable our access.