Start with the shape, not the colour
A legal skip is a rectangle. Steel-sided, one uniform colour, usually yellow, red or green depending on the hire company, and dropped square to the kerb or driveway because the lorry that delivers it needs room to swing the hook. Fly-tipped waste almost never arranges itself that neatly. It spreads, it piles, it follows the contour of whatever ditch or gateway someone backed a trailer up to. When you're scanning imagery across a verge or a patch of vacant land, shape is the first tell, before you've even got to colour.
Location matters too. A skip sits where a permit application says it should: a driveway, outside a house mid-renovation, near a known skip hire yard. Fly-tipping turns up in gateways, laybys, the back corner of a quarry, under hedgerows, anywhere a van can reverse in and be gone inside five minutes. If a pile sits somewhere a flatbed lorry physically couldn't deliver a container, that alone is worth flagging.
What texture and colour actually tell you
Fly-tipped waste is mixed-stream: builders' rubble next to black bags next to a mattress next to a run of tyres. In very-high-resolution RGB imagery that mix reads as a broken, high-contrast texture, lots of small shadows and colour changes packed into a tight footprint. A skip casts one shadow and shows one surface colour. A dump casts a dozen.
Tyres are an easy win once you know the pattern. Black rings, stacked or loose, show up at ≤0.5 m resolution as a distinct speckled texture that nothing legitimate produces. Scorched waste is another: burning leaves dark, irregular ground staining that spreads past the edge of the pile, something a skip never leaves because the waste never touches bare ground to begin with.
The other useful signal is change over time. A skip gets emptied on a schedule, you'll see it, then it's gone, maybe a fresh one in its place. A fly-tip just grows. Same footprint, same spot, more material every time you overfly it, because nobody's being paid to collect it.
When the imagery alone won't settle it
None of this replaces a site visit. Shape, texture and colour narrow down which of the flagged locations across a sweep are worth sending an officer to first. They don't replace the paperwork. A permitted skip on private land with a valid waste transfer note is legal even if it's sat three weeks longer than it should have.
The imagery tells you where to look. It doesn't tell you who holds the permit, who hauled the load, or whether the landowner signed off on it. That part still comes from your own records and a knock on the door.
Worth remembering too that a quarterly pass has gaps. A skip delivered and collected inside that window might never appear in the imagery at all, and a dump that's grown since the last pass is exactly what you want flagged, not a site you already actioned. Compare against the previous quarter before anyone drives out, not just the latest shot on its own.
If you're trying to do that comparison by eye across every verge, quarry and vacant lot in your jurisdiction, every quarter, it stops scaling fast. Waste Dump Detection runs that side-by-side for you, flagging the texture and colour signature of newly tipped waste against the last pass so you know which sites have changed since you last looked.
Worth setting up a quarterly pass before the next complaint beats you to the site.