This question is a year old, but I want to contribute for help other people...
Spring have ways to do the job that you want. Take a look in this chapter of the Spring 3x reference. Or Spring2x.
In resume:
You can obtain your image file from file file system of the server. As you can see in the reference:
Resource res = new FileSystemResource(new File("c:/Sample.jpg"));
helper.addInline("identifier1234", res);
Or from a relative path of the classpath of your application:
Resource res = new ClassPathResource("mx/blogspot/jesfre/test/image.png");
But, if you want to send a resource from a file server with a URL, you can do something like @Ralph said:
Url url = new URL("http://fileserver.com/images/123.jpg");
Resource res = new InputStreamResource(u.openStream());
And then, simply add the resource to your message:
helper.addInline("myIdentifier", res);
Hope this help somebody...