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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
    
Let me get this straight: In order to check for plagiarism you want to use someone's complex code, built at great expense, without paying for it? –  Daniel R Hicks Jan 5 at 23:49
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5 Answers

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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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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up vote 1 down vote accepted

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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You accepted your own answer, which paraphrases that of what harrymc offered? Rather than give harrymc credit? How ironic that you are looking for a tool to help you figure out when you need to offer credit to others. –  Bill Nace Jan 6 at 0:32
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@BillNace, what are you talking about‽ What does Ender’s answer have to do with harry’s? Did you bother checking the URLs/sites? They are completely different. Did you bother reading the actual text of the answers? Where in harry’s answer does it say anything about the Google API which is featured prominently in Ender’s answer? –  Synetech Jan 6 at 17:21
    
@BillNace I suggest you check where links point to before you throw around accusations. I accepted my own answer because for the purposes of checking general plagiarism this was the best option outside of a locked-in solution that the likes of universities use. –  Ender Jan 7 at 13:58
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I just recently researched a few of these online plagiarism checkers and found out that most of those free sites are using the Yahoo API to check for plagiarism in the backend. Although I found this overview pretty good, I'm personally using Google most of the times, as the results significantly surpass the ones by the Yahoo API-based sites.

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Plagiarism-Checker by architshukla on github is an (mainly) open-source plagiarism checker script written (mainly) in python, that advertedly/supposedly uses google api to n-gram check documents.

I haven't tested it but maybe you could check it out. It's intended to work on Windows and Linux.

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