Simple, Pop-up Images

I’m looking for suggestions:

I’m using the latest version of WordPress (I just love this product), but what it appears to be missing is the ability to insert a thumbnail image that, when clicked by a visitor, opens into a new window containing the full-resolution image.

There appear to be several plug-ins that do this, but they either don’t work on the latest version of WP, require uploads separate from the WP admin, require that you remember the fully-qualified URL, etc. I’m finding nothing that is as simple and elegant as the standard WP image upload/insert capability. I’m guessing that this is a very common need, so I must be missing the obvious.

Can anyone point me toward some solutions to this situation? I’ve got lots of high-resolution images that I want to share with my visitors, but which I want to restrict to 400px wide thumbnails in my posted content.

Thanks for any advice or assistance.

Steven