htaccess rewriterule to ignore prefix

i having problem creating rules that will ignore prefix on image name:

this is the request: http://mydomain.com/image/brakepads---sample1image.jpg

rewrite rule will ignore content before "---", web s开发者_如何学运维erver will serve this: http://mydomain.com/image/sample1image.jpg

Thanks in advance

---

RewriteRule image/(.*)---(.*)\.(jpe?g|gif|png|bmp)   image/$2.$3 [L]