I just had another thought: industrial machine vision systems come with all sorts of image inspection tools including such things as "edge detection". I wonder if this could be used in conjunction with a normal (not thermal) high resolution digital camera.
The general idea would be to:
1. take photos whilst on the move through a snare-infested area where a high res camera would be able to pick up a thin wire loop with sufficient resolution to make it visible;
2. let attached computer with vision software analyse images instantly for straight or looped edges that would indicate a snare.
What could help considerably is to take pictures in subdued natural light, maybe at dusk or dawn using a strong flash, possibly not just the built in flash of the camera but an external one. On the assumption that most snares are made from plain "shiny" metal, they should show up fairly well as "bright highlights" against the otherwise fairly dull (in terms of specular reflection) undergrowth. It would get more difficult though if the foilage was covered in water droplets as these would reflect the flash light, too.
I admit this is an idea that just sprung to mind and I have no idea how well this may work in practice. If you want to have a go yourself, set up a typical "snare scenario" and take some high resolution photos as described above from a few metres away. Then use free vision system software to process the images on your computer and see what you can find. Try this one, for example, https://www.teledynedalsa.com/en/products/imaging/vision-software/sherlock/
I have used it some years ago (for an industrial application) and found it very useful on early trials as it allows you to use all features processing images from a local folder rather than a live camera. This would be all you need to test whether there is any merit in this.
Sorry if industrial vision applications are not within your skill set but I thought I mention it here in case someone else wants to investigate it. I am not exactly twiddling thumbs otherwise I would be seriously tempted to have a look at this myself (pun intended:)).
Let me know if you need some more input on this,
P.S.: A rough calculation on camera resolution:
- snare wire diameter is, say, 3 mm
- target size in image of the wire is at least 6 pixels (to reliably show diagonal edges)
- 20 Megapixel camera image is about 5000 pixel wide
- then you could cover an area 2.5 m wide per image (5000 / 6 * 3)
> this may be a workable distance to cover per image.