Channel Form Validation

Hi,

I’m trying to add a rule validation of one Channel Images field in channel form. I’m using this code:

{exp:channel:form channel="mychannel" return="ENTRY_ID" error_handling="inline" rules:product_images="required" rules:tags="required"}

{field:product_images} 
{if error:product_images}<div class="alert alert-danger" role="alert">{error:product_images}</div>{/if}

I need the validation at form level and not a channel level, so product_images field (Channel Images upload field) was set not required at channel level.

Is there any way to set this field as required at form level?

Thank you.