I talk about this a lot of tumblr (where the majority of my original content is reposted from just based on the sharing nature of how that site works), but I don't think I've solidly addressed this here yet besides the small blurb at the bottom of my blog above the pixels which says, "Please do not repost or use my original content".
I haven't found it to be a huge problem here, and if you have done it, I'm probably not upset (unless you did it to purposefully annoy me, then FUUU), especially since you probably did it without knowing how I felt about it.
This particularly comes into play when my photos are used for the profit of others. I don't make any money as a blogger. I don't make any money as a "photographer" or copyright holder to my images. If I don't make any money from my photos, I don't think it's right for others with no connection to me or my blog to be profiting from my photos that I own and did not intend to be used that way, especially without at least sourcing my blog.
This all might sound kind of ridiculous, but I have literally seen for-profit businesses/working bloggers using my images in their advertising or on their websites. My blog was not sourced in any of these cases nor was my name was not mentioned anywhere. The closest thing was that someone said "from weheartit".
Which leads me to why I really don't want my images reposted. Period. Because even if my photo is sourced correctly on other sites (which is rarely is) like weheartit, chances are that the next person who wants to use the photo after seeing it on weheartit doesn't care. Like I said earlier - farther removed from the source, less likely chance that they care about the source, especially when it comes to weheartit -__-. And people like to source weheartit/pinterest/polyvore for some reason even if the actual source is listed in the entry. To me, that's like citing "Google.com". It doesn't mean anything and not at all indicative of where the photo is from/who the photo belongs to - just where you searched or found it. I don't think I can change that, so instead I want to try to let people know that I would ideally like it not to potentially happen at all by trying to ask that my photos not be reposted.
Just for the record, in my experience, watermarking does not stop people from reposting pictures or really help users find me as the source even if I were to write out my whole url on the photo. Most people who are reposting just won't take the effort to type it out and don't care. I only watermark because it can sometimes help when you are making a claim to your work, but it's not something that actually prevents reposting. And apparently many people who repost from reposters don't care that the watermark doesn't match the previous source.
If I file for copyright against you, it's not personal - I file as many as I can for the ones that I notice. I'm not trying to target any users in particular. The reason I might file the form instead of asking you to delete is that filing will get all the children of that post taken down as well (ex. repost on tumblr AND all the reblogged versions of that repost deleted vs. just the original repost deleted while all the reblogged, wrongly-sourced versions are still out there and able to continue to get passed around).
Also, if you added a filter or changed the lighting or something like that to one of my photos - please know that that does not suddenly mean that the photo is yours or that you are suddenly the source and can add your watermark and make claims to it. You might be the source of the edit that I did not ask for or want, but I am still the copyright holder of the image despite the filter - sorry.
If you have any questions about this, please feel free to ask in the comments.
[Note: I mentioned not making money as a blogger, but I recently added Ad Sense to my sidebar. However, seriously like no one clicks on it, and I don't ask anyone to because I know that's annoying and the point wasn't to make money anyway. Tbh, I only added it to see if I could and what would happen and how it would affect my blog. I'm not sure if it has had any effect. I personally don't even notice Ad Sense banners most of the time on any site, so it doesn't really bother me, but if it's annoying to anyone, lmk & I'll take it down because, like I said, I'm not actually earning money from it anyway lol. Seriously.]
Slightly on topic, if your work/photos have been reposted, and you want them removed from a website, here are a few quick links -
Weheartit - http://weheartit.com/contact/copyright
Pinterest - http://www.pinterest.com/about/copyright/dmca/
Polyvore - http://www.polyvore.com/cgi/copyright.notification
Facebook - https://www.facebook.com/help/contact/1409697672616547
Instagram - https://help.instagram.com/contact/391888707564685 (click "Continue with your copyright report" then "I found content that may violate my copyright" then "Please click here to continue with a copyright report")
Tumblr - https://www.tumblr.com/dmca
However, if your tumblog is the source of the reposted work, Tumblr's new policy is to email them instead of using the above url. My emails typically go something like this -
To: firstname.lastname@example.org or email@example.com
From: email-address-that-I use-for-tumblr-login
Subj: REPOST TAKEDOWN REQUEST
URL of repost - [insert URL/permalink of reposted photo on other blog]For more information about the Digital Millennium Copyright Act, the wiki page is not bad :)
My original post (source of photo) - [insert URL/permalink of your original post on your own blog]
Please REMOVE the repost from the other blog. Please LEAVE my own ([your url]) post as I only provided it as a source but do not want my own post taken down.
I did NOT give permission for my work to be reposted or edited.
[Your name and/or blog url]