Question about validate adult content in website/app

Hello,

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I am planning on creating a mobile app. It will alow users to post content: photos, videos (social media app like instagram).

How can i control the published content? Most APIs for validating adult content are expensive (in my point of view).

For images: Microsoft charges ~0,85€ for 1000 images

For videos: Google charges ~0,15 per minute of video (i think)

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It seems too costy to handle this… at least the video part.

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I thought about SMS account validation (only when the account is created). This should reduce the spam, but i do not know.

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The process of creating an APP like this one is too complex, but this part seems one of the most complex/costy ones.

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Do you have any alternatives? Or some suggestions?

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Thank you!