What is the ruling on a permanent tattoo over a large birthmark that has no cure and prevents marriage?

Tattooing is forbidden. However, if the birthmark is disfiguring or harmful, and specialists confirm that there is no treatment for it other than tattooing, then it is permissible to treat it with tattooing out of necessity. But it appears that tattooing does not treat the birthmark but rather covers it, which is closer to deception. One should consult specialists, as laser treatment for birthmarks has become available.