I have had some success using RNNLIB ( original , Github Plug ) which uses AI neural networks.
There is a demo link to the Github readme, as well as at http://www.cs.toronto.edu/~graves/handwriting.html
Example:





Please note that no demo has particularly good support for numbers (mostly unreadable), and uppercase letters do not cover as well as their lower counterparts. Sometimes the generated image may be missing letters or just go away.
Since this is based on a neural network, it is likely that some of these problems are the result of or can be improved by training the data.
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