Fine detail in the eye also increases value. Good documentation is needed to prove the origin of the jewelry. Where values climb, fakes follow. The example shown here is a cheap imitation using a computer image copied from a book. The miniature contains pixels rather than brush strokes.
Most fakes are more subtle.
Be wary of murky colors that use dark sepia tones. These show a heavy-handed effort to falsify age. On the other hand, some fakes are too colorful and should raise an eyebrow. Finally, remember that an antique frame doesn't add authenticity to the painting. The identity of the subject remains a mystery, but their beauty and novelty are no secret.