Why it shows warning?
Because it could not move the file move 'C:\xampp\tmp\php2923.tmp' to 'images/20140302_210804.jpg
Upload always put your file first to a temporary position, and then you are responsible to move it to the right position.
Maybe you should provide an absolute path in $upload
.
If error still there, you can check your filesystem.
If error still there, use php file functions to see if php can read and write the directories.