But, looking from Account, Contact and Opportunity perspective, it is not easy to identify which of them are converted from Lead. However, if you have field history tracking enabled, looking at the object history related list will tell you if the record is created by Lead conversion or not.
Opportunity Field History
This will be not ideal if you would like to run a report of Account or Opportunity with Lead conversion information, because that information relationship only available in report with type Leads with converted lead information.
Workaround: we can built a simple solution (without code), in this scenario, we would like to report if the Opportunity is created from Lead conversion, and if yes, from which Lead.
1. Create Custom Text Field at Opportunity
Create a custom text field in Opportunity, and make sure with 15 or more characters length.
2. Create a Custom Formula Field at Lead
This formula will return in Text format. The formula would be just a simple Id that will return 15 characters length of the Lead Id, or CASESAFEID(id) to return 18 characters length of the Lead Id.
3. Map Lead Field
From Lead field setup, map custom formula field at Lead to custom text field at Opportunity, this is fields we just created above.
Pretty easy, isn't it? From now on, we will be able to tell by running an opportunity report, if the Lead Id is not blank, the Opportunity is created from Lead conversion, otherwise it is not created from Lead conversion.
How to handle if user Clone the Opportunity?
A classic issue that we thought that the Lead Id will be bring over to the new Opportunity cloned, so the Lead Id information is no longer correct. This is only true if we add Lead Id custom text field in to Opportunity page layout.
This mean, Clone function will only clone fields that show in the page layout. By remove that field in the page layout, it will not clone Lead Id. See sample below:
As a double protection to make sure the Lead Id will never be cloned to the new opportunity:
1. Set the text field in Opportunity to 18 characters (for case insensitive Id)
2. Set the text field in Opportunity as Unique and not Case Sensitive
3. Set the formula field in Lead to CASESAFEID(id)