If the element is present on the UI, there will be some identifier.
You can try identifying a parent element and under that, you can identify the child element.
Also, you can try using XPath.
If the element you are trying to identify is not part of the DOM. i.e. it's Flash object or PDF, or any other type than HTML, you can not identify using selenium. In this case, you may use tools like Sikuli.
