For those who are planning to unroot, return/restore Samsung Galaxy S3 to stock, then you need a stock firmware that you can download here. Stock firmware that’s available here is a firmware to be used with Odin, so do not ever try to flash it using recovery. Since the firmware is an official from Samsung, then most likely the flash counter will not count this procedure.
By flashing your Galaxy S III with the stock firmware (ICS or Jelly Bean), then all the data, settings, customization, including all apps that you have installed previously will be removed, but your files that’s located on the SD card will certainly safe, since Odin only wipe the internal storage. However, it is advisable for you to have a Nandroid/ROM full backup before performing a flash by using Odin, but when you plan to return the device to store or even offer it for sale, then you’re not necessary to have a Nandroid backup.
You can get the stock firmware for Samsung Galaxy S3 on different variants such as Verizon (SCH-I535), AT&T (SGH-I747), Sprint (SPH-L710), T-Mobile (SGH-T999), U.S. Cellular (SCH-R530) , Canada CA Rogers/Telus/Bell/SaskTel (SGH-I747M) and Wind/Videotron/Mobilicity (SGH-T999V30) and International (GT-I9300) variants.
Be sure to download the stable build, not the leak firmware in case you’re planning to return this device for warranty. Do not forget to always use the latest Odin software to carry out a flashing.