Hi
Can you please explain you I.D please.
You're asking me if I'm sure or how I know what it is?
Yes, I'm sure.
Most experienced Australian herpers could just take a glance at this picture and recognise it without thinking about diagnostic features, much like most people don't really think about any particular diagnostic features when identifying a picture as a bird or dog or fish. The colour/pattern would immediately tell you it's somewhere on the east coast, or maybe somewhere else in northern QLD, but we were given the location anyway.
Some diagnostic features are the lateral body compression, scale count with enlarged dorsal row (we don't have anything else similar in Australia), the scale shape and overlap, the colour pattern isn't reliably diagnostic but immediately tells you what it probably is and everything else confirms it (I didn't think it through like this, I just immediately recognised it because I'm familiar with them, but if I stop to think about it I can see these things, just as you would describe a fish to someone who had never before seen a fish).
The scales are radically different from any python. Pythons all have much higher scale counts. An elapid would have a very different body shape (not are laterally compressed like this) and the scales would overlap more like roof tiles rather than a tesselation/mosaic arrangement as we see on this Boiga. The shape of the scales on the dorsal row are very distinctive. Australia has very few colubrids and no others are anything like this. Even by simply ruling out elapids and pythons you're left with only three species of colubrids to work with and it's clearly not a Dendrelaphis or Tropidonophis, leaving only one option.
And yes, to any pedants, I left out blindsnakes. Deliberately.