Could create it in Java in about 20 days (communication and all included).
By gallery I assume you mean Android device gallery with local images, and not something in cloud/remote server?
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Selecting photo from local gallery is easy, few lines of code.
There aren't that many system fonts, so I would recommend finding free fonts in .ttf and use it in application in order to increase number of choices.
Applying text, color, and fonts and then getting new image out of it can be done by using "canvas" in Android.
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Pure technical work might take about 5 days, but I extended it to 20 days since pretty often most time spent is communicating, but in case there are no issues you could expect to have it faster than that.