How I can protect my application against copying?

May be exist many ways. One of theme is using HD serial number.

1. Read volume serial number of hard disk(s) of your customer. ( Apply this procedure while installation, once only one and preferably manually.  Of course you can obtain this info by online accessing to system of your customer. )

2. Record this info ( after crypt ) anywhere you like in the customer system: in a .MEM file, a .dbf / dbt, in registry, even directly into your application as a literal constant.

3. Your application will begin to run by reading this recorded data and compare it with actual HD serial number of customer; if match continue working, else …

Here an example to get  HD serial number.