Blockchain solutions provide a couple of nice characteristics, based on the public ledger: high-availability, high-trust and immutable. Unfortunately, they sometimes lack of the industrial scale providing an cheap and easy way to work with the Blockchain, or simply the necessary stability or necessary throughput to deal with a huge number of transactions. There is however a way to integrate blockchain to existing systems with creating hybrid Blockchain solutions.
Let we have a classsical IT System, with a couple of standard transactions. Let we say that there are a couple of transactions or system states that are required to be saved and validated in a high-trust and immutable way. Well the natural way is to save them into the Blockchain. Examples might be archiving a document into some kind of a storage with the guarantee however that the data can not be changed or frauded in a later timepoint. The natural way is to calculate a hash (a fingerprint) for these documents and save it to the blockhcain. In this way the registrated fingerprint of the document can not be hacked or modified anymore and in the future it can be always checked if the certain version of the document matches with the saved fingerprint.