Hi,
Yes it's something which could be done with HikaSerial.
It would generate a unique serial and if you use the "consume" feature, you would be able to have a special "status" in your database in order to validate if the serial is real and if it has been already used or not.
www.hikashop.com/en/hikashop/138-hikaserial-consume.html
The AttachSerial plugin could read data from the order or from the product item. So you can create a custom field for the special message and display it in the image.
(But a little improvement should be added in order to manage when the text would be displayed outside of the image in order to put the rest of the message on a new line).
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.