Why does my husband's picture show up on my sister's iPhone when I call her?

Your sister can follow these steps to change the picture that appears when you call her:

1. Open Phone > Contacts > search for your name and open the contact detail.
2. Tap Edit.
3. Next, she can tap Edit under the picture and select a different photo.
4. Tap Done at the top, right of the screen.

Now, when you call her, the new photo should appear.

Have her check to see what image is set to his contact card on her phone. That is where it comes from.

Have your sister also check to make sure she doesn't have your phone number listed under your ex-husband. People do sometimes put spouses' phone numbers in the same contact card.