The short version. Three free previews a day, email verification required, no card. The preview carries a watermark and the print never does. You tick to accept a specific render before you can add it to the basket, and switching to a different render withdraws that tick, so it is not possible to agree to one picture and receive another.
How it actually works
Upload one photograph of the car. Choose one of nine styles. The picture is shown in your chosen style before ordering, watermarked, at screen resolution. If it is wrong, generate another or change style and try again, within the three free previews a day. When one of them is right, tick the box against that render. The tick is what unlocks the basket, and the checkout refuses a custom order that does not carry it.
After payment the same picture is used exactly as selected, without its watermark, and that file is what gets printed. This matters more than it sounds: the accepted preview is kept and used as the basis for the print, rather than the prompt being run again from scratch to produce a different picture at a larger size.
The nine styles
Four of them are painting: oil painting for old-master weight, watercolour for loose washes and white paper breathing through, vintage racing poster for flat lithographic colour in the language of the golden age, and pop art for halftone dots and hard-edged colour blocks.
Three are drawing: blueprint puts the car in white technical linework on cyanotype blue, the treatment the blueprint prints use; single line reduces it to one continuous stroke like the silhouette set; and designer sketch is pencil construction lines and grey marker off a studio presentation board.
Two are photographic in feel: garage noir is dramatic low-key black and white, and night drive is the neon and wet tarmac of the night drive pictures.
What photograph to use
A sharp, well-lit three-quarter view, front and one side visible, on an uncluttered background. Bright overcast light is easier than direct sun. What ruins a result is not resolution so much as clutter: another car half in frame, a busy hedge, a person leaning on the wing. The style has to interpret everything in the picture, so give it less to interpret.
Resolution is checked against the exact size you order rather than in general, and a size that would print soft is blocked before checkout rather than apologised for afterwards.
What it is not
It is not a commission. Nobody paints it by hand, there is no back-and-forth with an artist, and it is not the same purchase. It is also not a way to obtain artwork of a car you do not have a photograph of: the tool works from your picture, not from a description, and it cannot reproduce somebody else's protected design to order.
If the photograph is already good enough to hang as it is, printing it directly is the cheaper and more honest option, and the same resolution check applies. If you would rather have something already drawn, the art is the stage that covers the rest of the collection.