By default, the crafting block is still activated by placing a crafting table in the item frame on the dropper. However, any item placeable in an item frame can now be used. So, you can make it more challenging to create a crafting block by choosing a rare material such as dragon head, diamond block, or playable record. In the simplest use cases, set activationItem in the config to the name of the chosen item's material. See https://hub.spigotmc.org/javadocs/bukkit/org/bukkit/Material.html for material names.

If you wish to strongly control who can create crafting blocks then you will want to choose an activation item that cannot be gathered from the world through normal means. In this case, you can set the activation item to a serialized ItemStack specification in the config.yml. Below is an example that forces the use of a crafting table with a specific descriptive "lore" and plugin-specific NBT data. Use the /craftmatic:give command to get this block in-game. The use of the give command itself is controlled with the craftmatic.command.give permission.