This may sound silly, but an external device could probably convert interfaces from USB to CD. So will I be able to install OS from USB if I buy a card reader?
It really depends on the system and the chip used inside the card reader.
The BIOS has to support the device as a bootable device, and, many just support a very limited number of devices.
If you put it in and it is available as a bootable device option, and you then format the device with an active partition and include the setup files - most likely you will be able to.
That being said, you are much better off just buying a USB stick and installing to that as most BIOSes support Mass Storage booting.
Install? Depends on the OS. It is possible to select the installation medium source for some of them. Boot? Much harder. Completely dependent on the BIOS.