please could you help me?
i have an arduino uno r3 atmega328 i tried to put it in dfu mode many times but it wont
this the picture of my arduino i think it cloned
That's a clone that uses a CH340G, not a 16u2. The 16u2 is a microcontroller, pre-programmed to act as a USB Serial adapter (and so you can reprogram it using DFU or ISP), whereas the CH340G is just a serial adapter. Most clones don't have the 16u2 (probably 99% of users never reprogram the 16u2).
Since there's no 16u2, there's nothing to put into DFU mode. It is not usable for any project that requires modifying the firmware on the 16u2 (which is what you update using DFU mode) because there isn't a 16u2 on the board.
To find Uno clones that do have the 16u2, search ebay for something like "Uno R3 16u2", and verify that the picture shows a 16u2 (the chip near the USB port, the 16u2 is square, with short pins on each side, not rectangular with pins on only 2 sides) and that the description says it uses a 16u2, and doesn't mention using CH340G or FT232.
thanx alot..........