First of all img elements do not have closing tags (i.e. </img>). They are self-closing. Also, you can not use flex-fit or self-justify properties unless the parent element has display: flex as a property.
In what way do you want to resize the image? You were not specific in what you are trying to accomplish.
Either way, I suggest you take a look at our Responsive Web Design curriculum where you can learn more about proper img element syntax and how to use flex-box in your CSS.
There are no such properties. For what you have as flex-fit you may be thinking of flex-basis, or at least that is a property that would let you set a presentage value. For self-justify you may be thinking of justify-self, however that doesn’t work with flexbox, only align-self works with flexbox.