@Bondi Beach
I used one image I already had for Harper, who appears on her own and in a longer story. I remember thinking, "that's her!"
Yeah! That's it for me. For some characters I have a picture that captures both looks and personality, and that really helps. Others, it's harder, and, for a few, I have a couple of pictures each suggesting different aspects.
Separately, I've never seen it work for the storyteller to say, "Well, she looks like / reminds me of [insert name of well-known singer or actor]."
I've got one character that I picture that way, and even have pulled a photo of, and interestingly it's a male character who is modeled after a country music singer. BUT, I'll never use that in a description. I don't like it when I run into it in a story, especially when I often have to go look up the referenced person. That sort of specificity is just too much for me. The suggestions of some of the authors on here to be more vague and to focus on the impression the character inspires in others seem to work well when I read them in stories.