I haven't used the app. On the pc there is a slider right above the image that lets you decide what selection value you want it to allow. I don't think it appears until you load an image. Softer images require lower values. Obviously the more crystal clear the image the better return you get. I have occasionally chosen one or two very distinct letters and hand traced them out to submit so I could get the whole font. Doesn't always work but a little effort makes a difference.