Telling the difference between a Natural or Treated banknote is certainly not easy and virtually impossible to tell without having the note physically in your hands - so a photo really isn't any help, keep this in mind when buying anything from a photo.
Natural notes are generally nice and crisp with a firm thick body and what almost feels like micro corregation if you run the note between your thumb and forefinger. It is a natural characteristic of the paper Australian bank notes and it should always be present but can be more prominant from note to note. Telling the difference between treated and untreated notes is extremely tough and can take years of experience to master but there are a few things you can check which can help.
1. When you run the note through your 2 fingers it feels very flat and has a 'dead' feel to it.
2. If the note has a faint chemical oddor.
3. If the note is very limp and the paper feels quite thin and what I describe as sad.
4. Measure the note and see if it matches the correct measurements, if it is too big it may have been stretched and too small it may have been trimmed. Stretching can be used to removed creases and is generally done by wetting the note and then slowly stretching it flat. Trimming is used to tidy up a note if it has little edge knicks or is brown around the edges then it is trimmed making it look a great deal nicer. Another thing to check although I have found to be not as common is when a note has been stretched and then trimmed back to normal you can tell this by check the measurements of the coloured section of the note excluding the white borders which will tell you if it has been stretched and trimmed.
Something else which can be really helpful is if you have a note that you think may have been treated then if can get a hold of an identical note and by having the two too compare it can make it a bit easier. If you are unlucky and both the examples you have were treated then it obviously isn't going to be much help.
You can also always take it into your local coin dealer, many are more than happy to help.
There are always going to be cases where you just can't tell and of course heavily worn notes are going to be limp no matter what.
I would like to thankyou Michael from Global Coins in Brisbane who gave me my tutorial which was really helpful and allowed me to weed some treated notes out of my collection.
I you have any questions please let me know.
Regards, Michael Cotton.