Repeated visual clues allow us to follow the story in the images of the trial and the Africans' repatriation.

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Korzak and Redling say investigators routinely identify both technical and visual clues in videos for evidence to identify criminals and to rescue victims.

CNN: Pretzel bag narrows search for child abuser to U.S.

In many regions of Mars, dust-devil tracks and shadows have been seen from orbit, but those visual clues have not been seen in Gale Crater.

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Others have put forward different ideas for how pigeons find their way, suggesting that the birds use smell, visual clues or the Earth's magnetic field, or even a combination of all of these.

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