Customizing the display of an erroneous individual field

All the gogole (and forum) literature about this subject explain how to
easily modify the style, or add an error message above the field…
wworking good !

However I have a table in my form with for each line :
col1 is a picture, col2 a label and col3 the field,
when getting an error , I want to change the picture in the col1…

I don’t know where I can find information on trapping the error process
to be able modifying it…
as I can do easily in ‘error_messages_for’…
where can I find info on it ?

thanks a lot for your suggestions

joss