[TYPO3] TCEFORM: alt-tag mandatory only if an image is selected (tt_news)

[Sven Hary]

Hi List,

is it possible to make the alt-tag of an image mandatory ONLY if an image is 
selected?

with
TCAdefault.tt_news.imagealttext.required  = 1
it's only possible to make it mandatory by default. But thats not so smart, 
if no image is selected.

Thank you

Sven Hary