While it is trivial to convert your string of hexadecimal characters into actual numbers, to convert that into an image, we would need to know how the image is actually encoded (Size? How many colour planes? If more than one colour plane, are they interlaced or consecutive? Row major or column major? etc). There is no convention for that.
It would also be useful to have an example of your text file (not a screenshot, the actual file!)
