Is it necessary to download UNetBootin or other softwares to create a live os on a usb?

I was trying to download Tails on a USB stick and as always, you have to download the file (in this case a .img), but then I was told that I had to use software to make it work (I was recommended to use UNeBootin). This is where I am confused. Why do I actually need it? And can I download tails without it?

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Author: John Doe