If your photographing outside on soft ground , and they got short boots on , you can use stiff wire shoved up the trousers one end , and the other end of wire stuck in the ground . If they got tall boots on you can drill a hole through the sole of the boot and do the same . I have used cut up wire coat hangars for this . For indoors if your able to use the "clone " tools in photoshop , you can use some small support and clone out the support so it`s not visible in the end photo .
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" There will be no Mercy ." Chip Hazard .