code: public boolean addTag(String tagName, String tagValue) {
      boolean result = false;
      if (firstIFD != null) {
        if (firstIFD.containsTagId(TiffTags.getTagId(tagName))) {
          firstIFD.removeTag(tagName);
        }
        firstIFD.addTag(tagName, tagValue);
        createMetadataDictionary();
      }
      return result;
    }
docs: Adds the tag.
  
  @param tagName the tag name
  @param tagValue the tag value
  @return true, if successful