Writing a texture to an ObservationWriter

Hi, i'm currently working on a game in wich the player has to draw a symbol, and depending on the symbol he draws the game is going to do an action or another, I want to create an AI that can identify symbols, and I thought i could feed the AI with the Texture2d that the player draws and feed it the original simbols, for that i planned on using an ObservationWriter() with the mlagents extension in order to accomplish that, but I tried feeding the Texture2d with the function writeTexture(), but it gives me errors, How can I feed the observation writer a texture2d?Is there any other way the AI learns about the symbols, any other way to feed the AI with the Texture2d?