Knots default settings do not allow you to attach enough data to a bitcoin transaction to attach a picture larger than 16 pixels to it.
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core is moving toward removing default limits such that you could attach images and or low->med quality videos to a bitcoin transaction with relative ease.
people are concerned about making this easy because they think people will put sick stuff on the blockchain. they would prefer to make this as difficult as possible, even though it is not entirely unstoppable.