How to embed scanned images to invoices?

How to bring in scanned images as inserts in invoices or quotes and e-mails?

This is not supported. What are you trying to achieve?

Sometime customer needs a diagram of what I have described in text with dimensions and it is safer to send diagram as an insert to avoid misplacement.

I think this is out of scope. At least for the foreseeable future. I don’t think any general-purpose accounting software is capable of this anyway. Just send your diagrams as separate documents with an invoice.

I have requested the facility to attach references such as scanned images, PDF, text documents etc. to quotes and I know this is on its way. I think this might satisfy munidasaraja. See Creating Reference Links to Sales Quotes.