You need to use your file manager app or something like ES file explorer. All you have to do is locate the files you want to move, select them, go to the menu and select "copy". Then navigate to the folder you want them in, and "paste" them there. And yes, you can copy (or move) photos to the Camera folder... at least it does on my Note 4.
Note that you should always use the copy function and not the move function. Android deletes the file in the original folder when it moves it... regardless if the move is successful or not! Always use the copy function and verify the files copied over correctly, then go back to the original folder and manually delete the originals.
By the way, you can also do it directly in the gallery if your phone has that function in it's menu. Just select the photo, click on your menu and see if the function is there.