Moroni 7:14 says:
Wherefore, take heed, my beloved brethren, that ye do not judge that which is evil to be of God, or that which is good and of God to be of the devil.
When one desires so strongly to connect to God that he uses an image or object that appears to represent a prophet or God, and when she is unable to admire or worship without it (that it infringes on the connection that exists without the image or object) then it truly has become a graven image, no matter how harmless or even uplifting the image or object is otherwise.
On the other hand, if it does not interfere with direct worship, I have a hard time labeling it as a graven image. In that case, it simply becomes a religious symbol - and religious symbols are both important and powerful reminders of deeply held faith and commitment. If a friend were to give me a cross, for example, as an expression of their realization of how important Jesus is to my faith, I would have no problem wearing it as a token of that faith - and I would be grateful for the feeling and recognition behind the gift. It certainly would not constitute a graven image in how I would use it.
(Thank you, MH, for prompting me to count my published posts and realize this is #300.)