Makes Duplicate Of File When Opening Pictures On A PC

I have photos and an external hard drive. When I either select the photos in the library and drag them to the desktop, or select the photos and do an export it does export the files to the external hard drive. When I open it on the mac there is only 1 of each file there. When I plug it into the PC and view the folder with the files in it there is a duplicate of each. The weird thing though is for example if I have a file named picture1.jpg it has that in there but also creates a ._picture1.jpg
What does it create that duplicate file with the ._ before it?
When I plug it back into the mac that ._ file is not there.


Mac OS stores "resource forks" (icons) in image files but PC users get two files when they are shared via HD, CD and even when using a PC to view the contents of any Mac directory on a PC.
My simple fix is to "delete" the resource fork prior to sharing with PC users so they don't get confused.
CMM's can do this with a right click prior to sharing and most image apps can also delete that resource fork file.
Mac Mail app allows the "Send Windows Friendly Attachments" which also removes the resource fork file so viewers are not confused.