Your scanner probably came with software that knows how to write scanned files to a file system. The most basic integration would be to simply mount the Alfresco repository as a shared drive using CIFS/SMB or WebDAV, then point your scanner software at that shared drive. When documents are scanned they'll go directly into Alfresco.
Some scanner software can integrate with document repositories using an industry standard called CMIS. Alfresco supports CMIS 1.0 as well as CMIS 1.1. If your scanning software can use CMIS, that will allow you to capture not only files but also metadata. So, for example, if your scanner software allows you to "index" scanned files, which means it provides a user interface for capturing metadata, like maybe customer number, invoice number, etc., that metadata can be written into Alfresco as property values which you can then use for search purposes.
It isn't clear from your question, but what you may also be looking for is something that can OCR the scanned document images. Doing that would allow the text of the scanned document to be full-text indexed. Your scanning software may offer OCR features or it might leverage open source OCR functionality. If it does not offer OCR features you might want to look at something like the Alfresco Simple OCR Action, which would allow you to convert the scanned document into text.
Hopefully this gives you some ideas. If not, please follow-up with more detail about what exactly it is you are looking for.
