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I am writing a dissertation for my final-year project and I know that regardless of what I write there are going to be similarities to stuff out there on the web and in academic journals and books. Thankfully for most Google can root out most of these with ease so finding a free plagiarism checking script shouldn't be too hard.

After a bit of Googling I came across a couple of really basic checkers, but most of these are either "basic versions" that require one to pay for a script that actually works or are just generally useless. I've found one that seems to work well for small chunks of data but fails miserably when handed a large file.

All I want to do is to be able to upload a Word document (or just input text if no upload options are available) and to tell me what appears to be copied and where from. Does anyone know of any good plagiarism checkers that can be downloaded for free or run online?

EDIT: Just to clarify my needs, I want a tool that can take a Word document and search it in its entirety so that it can label any instance where the document matches another document on Google.

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Wait, now I'm confused: you're worried about plagiarism in your own dissertation? Unless we are talking multiple personalities, then it's not really plagiarism you are concerned with. You might be worried about inadvertent borrowing or phrases (I've done that in papers), but rereading your own work carefully (and that of your sources) should save you from that. – Telemachus Dec 22 '09 at 1:57
I'd agree if it were a small piece of work, but aside from pure plagiarism I'd like such a tool as a form of quality control to ensure that everything I have written is in my own words and that the tone of the dissertation does not deviate between what I know and what I've read/paraphrased in an academic paper. It'd be far easier to write quality content if I know that what I'm writing is legit, especially when the sources begin to mount. A number of my professors use the institutions software to check their own papers over, but I obviously don't have this luxury. – Ender Dec 22 '09 at 2:02
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You may find different tools work better for different topics. Lots of r+d has been done on identifying key phrases for medical topics (with many medical terms). There may be no single tool which will work every time. – Russell Dec 22 '09 at 4:43
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7 Answers

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I don't think that you are going to find a real solution in the form of a script or a free application. Think of what you want the program to do: read a document and check for - what? (Other people's published work? That requires a big honking database of published works. Stylistic variance beyond some statistical norm? That requires a statistical norm for style (probably based on vocabulary and sentence length computed in relation to significant words - i.e. filter out 'and', 'or', 'to', 'for' etc.). These are not trivial requirements or something you can just put together in a couple of hundred lines of |insert-your-scripting-language-here|.

Many schools use Turnitin, and many schools use Google to search for published works. That method is hit or miss, for obvious reasons. Turnitin isn't free, and Google is a very imperfect solution, but those are the two solutions I see most often.

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Google indexes many technical books as well as many of the leading journals, so Google alone would probably find everything I need. It's just a shame that there doesn't seem to be a free program which can handle something like this. – Ender Dec 22 '09 at 1:53
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Key phrase extraction is not a new research area, and takes a lot of effort to develop potential solutions. They are going to charge to get reward for their effort in helping you solve your problem. (google.com.au/…) – Russell Dec 22 '09 at 4:40
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up vote 1 down vote

The University of Virginia makes available this tool: Copyfind.
Both source and executable are available for download.

This program examines a collection of document files. It extracts the text portions of those documents and looks through them for matching words in phrases of a specified minimum length. When it finds two files that share enough words in those phrases, copyfind generates html report files. These reports contain the document text with the matching phrases underlined.

What copyfind can do: It can find documents that share large amounts of text. This result may indicate that one file is a copy or partial copy of the other, or that they are both copies or partial copies of a third document.

What copyfind cannot do: It cannot search for text that was copied from any external source, unless you include that external source in the documents you give to copyfind. It works on only purely local data it cannot search the web or internet to find matching documents. If you suspect that a particular outside source has been copied, you must create a local document containing that outside material and include this document in the collection of documents that you give to copyfind.

For web checks you might have a look at:
Free Online Plagiarism Detection System, Plagiarism checker

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There are a lot of good suggestions here, but the general consensus is that there are no tools out there that can do what I want. Despite this, I have decided to carry on using the basic version of The Plagiarism Checker. It works almost exactly how I want it to, although to get some of the better features I would need to pay.

This tool uses the Google API and will find copied text extremely well, and I have already found two instances where I have written phrases that are similar to certain papers.

As others have listed some other great examples I may end up writing my own script to do what I want as I have working experience with the Google API and it appears that this is the best script available right now, with some of these scripts and techniques being the best for their own uses.

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Scripts can be written to interface with Google fairly easily (See Plain Google). It may require some hosting costs and some development time (long weekend most likely).

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Google

EDIT: Before this gets downvoted let me add that this is what my High School did. It proved to be an effective solution and very cheap. Just take the first sentence or two of a paragraph and BAM. Now I'm not saying this is fool proof, but it does work.

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Oops! Too late. – Lucas McCoy Dec 22 '09 at 1:46
This is what I currently do for small bits of work around 2,000 words, but this is no solution for a 25,000+ word document. Even if I could do this as an automated script it would be overkill and would probably get me banned from Google for excessive use. – Ender Dec 22 '09 at 1:47
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There's no reason to downvote this. You don't enter the whole 25,000 words into Google (for crying out loud). You pick phrases that betray another author and judiciously search for them. It's a somewhat painful and hit-or-miss method, but it's a pretty common way to do it in my experience. – Telemachus Dec 22 '09 at 1:52
Even what you're asking will take an extremely long time when a simple script could do it in seconds. In lines alone I would need to make around 2,500 Google searches to get a minimal return. Even if I wanted to do that with Google they'd kick me off for excessive use. Just picking phrases isn't a good enough solution for my needs as I want the structure to be critiqued as well as whether I had stolen a line or two. – Ender Dec 22 '09 at 1:57
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@EnderMB: You really aren't listening. A 'simple' script couldn't meet your requirement at all, and a script that could would need a lot mroe than seconds to do its work. – Telemachus Dec 22 '09 at 2:39
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You could be interested in these two sites:

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Both of those handle "plagiarism" on web pages. I'm looking for a solution that will check my Word document to highlight where parts may have been copied. – Ender Dec 22 '09 at 1:46
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Check out http://dupeoff.com It breaks your writing down to sentences or smaller chunks and queries Bing.

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