In the SEO field, one of the common issues that website owners have to deal with is other websites copying their content i.e. plagiarism. All of the content on ManningMarketing.com has been written by myself. The only page that I did not write was the privacy page, for this I used a privacy page template maker. So, I have roughly 80 plus pages of content that have taken a fair bit of time to write.
The big issue that the other website copying the content will come up with duplicate content issue right off the bat. So right from the start they are starting on the wrong foot, and they are not helping themselves out at all. Eventually they will be found out by the original writer of the content, and when this happens are usually a few ways of going around this.
The recommended way (by the search engines) is to email the website owner directly and notify them of this issue. Most the time they will comply with your request, but there will be cases where the website owner will deny copying it or you do not receive response from them at all. When you have to deal with websites that will not take down your content, the next step is to contact the search engines with a DMCA request.
For website owners that copy content and will not remove it, this is where it can get a bit sticky for them. When Google does comply with the request, the page will be removed in accordance with the Digital Millennium Copyright Act, and then the website owner will need to go through the process of getting their page reinstated once they have shown that they have made the changes.
So, to help with backing up your claim, You will want to see if you can get a copyscape report. The website is useful sometimes capturing some of the copied content, and when it does, it will plainly highlight all the copied text and you can share this URL to show to the search engines outlining the exact content that was copied. The single best way to find pages that have copied your content, is to search for bits of the content in quotes in the search engines. This will most of the time show more results than Copyscape.com. With Copyscape.com, you only have x amount of free searches per month, so use them wisely.
Another option is to check the website archive.org, this website will often have copies of your website (if not blocked via your robots.txt). The only issue with this is that can take sometimes the 24 months for them to display the crawl data, so this itself cannot always be a reliable source to back up your claim.
So even without archive.org, you can still go through the process, and most of the time things will work out in your favor.
For additional ways of Copyright protection, you can check out copyright.gov there also is an extensive FAQ list http://www.copyright.gov/help/faq/