@Nullable
  protected String getTargetImage() {
    String propertyAlternate = getProperty(PropertyNames.TO_IMAGE_ALTERNATE);
    if (propertyAlternate != null) {
      return propertyAlternate;
    }
    String property = getProperty(PropertyNames.TO_IMAGE);
    if (property != null) {
      return property;
    }
    return to.image;
  }
Gets the target image reference.

@return the configured target image reference
jib-maven-plugin/src/main/java/com/google/cloud/tools/jib/maven/JibPluginConfiguration.java