shared images folder for multiple website under one solution.

Please see my comment to the question.

The simplest solution would be to have one single site. But perhaps you want to have two sites really independent, first of all, one different domains. Then they can be served on different hosts by different servers. What to do in this case?

Another simplest solution would be having all those images on one of the two sites. The other site would use those images via Inline Linking: http://en.wikipedia.org/wiki/Inline_linking[^].

Isn't it really simple? Also, you can dedicate another side to those shared images. It can be served on a separate host, or on the same host as one of your two sites?

Moreover, you can even prevent inline linking by other sites. This can be done by some server-side technology. The image will be served through some server-side code/script which can check up the HTTP request for legitimate IO address or referrer and deliver content only to the legitimate requests.

—SA