Photos transfer from mac-book air to a hard disk

I have 7800 Photos on my photos of mac-book air, i need to transfer all the 7800 photos to a external harddisk. I created a separate folder with all the 7800 photos on the desktop now when i try to drag and drop the folder on the harddisk location it pulls back the folder to its original place. The hard disk has enough storage to accomodate the photos i am trying to transfer and the Format of the harddisk is Windows NT File System(NTFS). Please suggest