From the dark-alex psp wiki:
On the newer M33 firmwares, there has been an option to directly rip UMDs via USB. This method was more useful, but at the cost of your computer's memory, and space, it can sometimes prove costly for a while. To perform a backup via this method, you will have to boot into the XMB, and open up the vshMenu. From there, go down to the 'XMB USB DEVICE' option, and press left once to make it say 'UMD Disc'. From there, exit, and pop in an UMD. When it is recognized by the XMB, make a USB connection. When the connection is active, copy and paste the 'UMD9660.iso' file under the mounted drive to a selected directory on your computer. This process can yet again take 15-30 minutes depending on size, and the quality of the disc.