http://jamiethompson.co.uk/web/2010/05/15/google-streetview-static-api/

<<It is possible to extract both thumbnails and higher resolution images (tiles) from the Google Streetview service through an unpublished, undocumented API which I will document below. Google have not publicly released this API, but nor have they sought to secure or even obfuscate it in any way. To me, this is about as open an invitation as it gets.>> May 15, 2010

via HN

Below are some items from the above linked page by Jamie Thompson.

Zoom Level 2
http://jamiethompson.co.uk/wp-content/uploads/2010/05/zoom2.png

demo
"I’ve put together a very quick and dirty demo page that displays the tiles re-assembled for any given UK postcode. Be warned, at zoom level 5 this will download 338 512×512 pixel tiles, roughly 7-8MB."
http://geo.jamiethompson.co.uk/streetview_tiles.php?postcode=SW1W+9TQ&zoom=3

I don't think you can call that a real API, it's just "playing with parameters".