Embedding photo spheres has been a painful and annoying process since Google announced the ability way back when (and then stopped supporting it in Views). Today, the Google Maps team is making it a lot easier, using the Google Maps Embed API to get the job done. Take a look!
To embed an image like this one, simply open Google maps, and then switch to the Street View overlay. Photo spheres are highlighted in street view specifically as little bubbles, but you can also do this same embed method for any street view image and get the same 360-degree viewer.
When you're on the photo sphere or street view image you want, simply hit the settings cog at the bottom right of the interface and an option to share and embed will appear. Then, just insert the iframe code into your page's HTML. Easy. You can also just generate a hyperlink to the image to share.
Very cool stuff.