I'm trying to make this answer as 'meta' applicable as possible.
Using snippets / bits from other projects
Clearly mark the code with the original author's copyright. Make sure that your license of choice is fully compatible with the license of the code you are using. You will need permission of the author to move the code to a different license (unless they specifically allow you to do so, I.e. "GPL 2 or any later version")
Your program should have an AUTHORS file (or similar), where you list all contributors and things that you used from other projects.
Forking a project
For each module that you substantially change, add your copyright under the original author's. The same thing goes for licensing, you are bound by the terms of the license that was in effect when you forked it. If the project says "GPL2 only", you must respect that, you can't go to GPL3 without their permission.
This varies, greatly, depending on the license at hand. The QPL says you can only distribute changes in patch format, for instance, so make sure you understand the terms that allow you to distribute modified versions of the software.
Beyond that, always preserve copyright. If adding your own copyright to what exists, be sure that you clearly mark exactly what you are claiming.
You've got some options, jump to the end for the summary.
So let's break this one down...
Copyright (c) 2012 [Acme Corp]
This is the Copyright notice and it belongs to Acme Corp. It was claimed in 2012, which is relevant because Copyright does eventually expire.
If the claim was actually given to "Acme Corp", ie. it was boilerplate cut & pasted from the MIT example, then you could almost claim that there is NO copyright on this work. Acme Corp is a fictitious organization, and failing to update the boilerplate puts the claim on dubious grounds.
But let's be good citizens, and grant the copyright to the actual claimants.
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
This next section, the Permission notice, is stating that you can do just about anything you want with the code, including modifying the licensing agreement! The catch is that you can't change the license on the existing code - you can change only what you modify.
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
This part simply means you have to persist the notices that are above.
So, what can you do?
- You can and should lay copyright claim to the code you wrote and / or modified.
- To do so with the same MIT license: Just add your copyright notice after the 2012 Acme Corp copyright notice in the files you modified.
- You can license your modifications under a different license, if you so choose.
- To use a different license: Add your copyright and license notice after the entire 2012 Acme Corp block (copyright, permission / license, exclusion of warranty) in the files you modified.
In the simplified case of your question, here's what you need to do:
Emphasis added to highlight the differences.
Original work Copyright (c) 2012 [Acme Corp]
Modified work Copyright 2012 Steve Bennett
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
Best Answer
The license for that plugin doesn't say "Copyright (c) 2013 Keith Wood." It says:
I would imagine you could simply leave it just like that. If you want to include your company name, you could simply say:
The MIT license simply states that existing copyrights must be preserved. In other words, don't remove someone else's copyright notice. This, of course, doesn't preclude you from adding "portions copyrighted by [me]" to the copyright header.