Stegano 16
That's not a string of hex chars that you've cut out of the image, it's a string of indiividual letters and numbers seperated by spaces.
It's not a big jump in logic to work out how to turn that srting into the right format, so that it can be decoded.
Then it'll be pretty obvious what the last step should be reguarding the gif.
LOL I assumed the challenge required playing around with the nulls in the original image, I thought that's what it meant by playing with the spaces (the nulls (00) convert to dots in the string). I didn't even play with the latter half of the file (the important one), I just kinda deleted it and tried to make sense of the top remainder (i.e. I was using the wrong section).
If that's all that I'm supposed to do, then this challenge is super easy. I did actually do all that's required and got the right decoded string, but the output GIF is not viewable (I get an error from my image viewer).
With a few simple lines of code, you could output the decoded data diirectly into the correct format, or maybe try something like notepad++, or better yet get a decent hex editor like Winhex.
If you're saving the data in something shit like notepad then you'll lose some characters and after saving it tthe image will be corrupt