implementation of Digital signature in Sales invoice?

Dear Experts,

We want to implement digital signature for our invoice,

Prerequisite : Digital signature in BMP format

Integrate the same in SAP through smart Forms.

Just wondering do we have to implement third part software for BMP and then integrate? Is this one time activity? or Daily basis we have to scan the signature and then integrate in SAP?

Bit of confusion will appreciate help.

Thanks,

Nik