How to bind to ICloudBlob or some other (not string) type

We need to improve the template here, this is a common pitfall you've run into (sorry about that!). We're fixing, see the GitHub issue: Make it easier for users to get started with binary blob triggers.

There's a built-in template that binds to streams. Go to New Function and select C# for language and Samples for Scenario.

For a more advanced sample that uses CloudBlockBlob bindings (which requires the InOut binding direction that is not yet documented), see the Functions sample in ContosoMoments: DeleteImages Function.

Note that you can browse all the templates in the GitHub repo: https://github.com/Azure/azure-webjobs-sdk-templates.