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No, pixels have to be sold in blocks. Selling a pixel 1 at a time would be very inefficient. If you make a pixel for $1, then it could be that the transaction costs would amount to %30 or more. Also, it would not be attractive for advertisers, because you cannot put an image on 1 pixel. A pixel is no bigger than the dot at the end of this sentence.
This is a good suggestion, and one that we would like to incorporate in the future. However, it will be some time before this feature is added, as it will need a more advanced billing / accounting system and also a system for dealing with and tracking fraudulent clicks.