I created a photo library in SharePoint 2010 with LOTS of photos going into it. I use windows explorer view to drag photos from the server to the library. The photos all show checked out to me, and I want to check them in (and possibly disable the check-out/check-in feature altogether.
There are a couple of things to check to ensure documents are not automatically checked out:
1) Go to the Library Settings and ensure there aren't any required fields
2) Go to the Library Settings > Versioning Settings. Ensure content approval required is turned off and require check out is turned off.
To check-in the ones you already have checked-out, you will need to select them all in the web browser and click check-in on the ribbon. Alternatively, you can use SharePoint Designer to connect to the site and check-in the items (this may be easier for you doing it in bulk).