You want to store them somewhere, though that could be in a Sprite added to the Stage if that is easier. If you want to refer to them later then storing them separately could be useful.
Also be aware your getImgFromRepo
when called twice with the same name gets the same image. So if you do this:
flower1 = getImgFromRepo("flower")
flower2 = getImgFromRepo("flower")
flower1.x = 50
flower2.x = 100
There is only one flower Image, which is at x == 100 as that is the last position set to. If that is not what you want then just doing
new Image(tat.getTexture(imgString));
Is safer and has minimal overhead