Online, the photograph is all you have. It carries more information than most people extract from it.

What to look at

1. The drape. Look at how the fabric falls from the shoulder or the waist. Good fabric hangs in soft, irregular folds. Poor fabric either stands away stiffly or clings flatly with no body at all. This is the single most informative thing in a photograph.

2. The sheen. A hard, uniform shine across a whole garment usually means cheap polyester. Natural fibres and better synthetics have an uneven, softer lustre that varies with the fold.

3. Pattern matching at the seams. On a stripe, check or print, look at the side seams and the centre front. A pattern that continues across the seam means the maker used more fabric and cut carefully. A pattern that jumps is the clearest single marker of a cheap garment.

4. The lining. If you can see inside, a lined garment is a better one — a lining costs fabric and labour. On a coat or a blazer, absence of lining is a significant saving being passed to you in quality terms.

5. The buttons and hardware. Zoom in. Thin, shiny, moulded plastic buttons signal a low unit cost. Weight and finish on a zip, buckle or button correlates strongly with the rest of the garment.

6. Where the model is pinned. Look at the back of the garment and at the waist. Bunching, an unnatural fold or a hand conveniently placed at the small of the back often means it has been clipped to fit. Standard practice — but it tells you the fit is not what it appears.

7. The number and type of photographs. Multiple angles, a detail shot, a fabric close-up and a movement shot suggest a retailer confident in the garment. One front-facing photograph on a plain background, especially with no close-up, is a signal in itself.

8. Flat-lay versus on-body. A garment shown only flat is hiding how it hangs. Ask why.

9. The description length. Retailers who describe fabric, construction and fit in detail generally have more to say. A two-line description on an expensive garment is worth noticing.

What a photograph cannot tell you

Be honest about the limits. It will not tell you the weight of the fabric, how it will wash, whether it will pill, or how it sits on a body unlike the model's.

For those, go to the composition label and the reviews. Reading a composition label covers what the percentages predict, and reviews mentioning fit are the most valuable text on any product page.

Putting it together

For a cheaper version of something you have seen, the useful comparison is not price against price. It is drape, pattern matching, hardware and lining, side by side.

Sometimes the cheaper garment is genuinely the same thing at a better price, because the saving is in the brand rather than the cloth. Sometimes every one of the checks above explains the gap. Knowing which is the whole skill, and it takes about a minute per garment.

If you would rather not do it manually, DUPI reads an item from a photograph and searches real UK shops for the same look at a friendlier price, with the prices and links checked. How to find a dupe sets out the manual method in full.