Image background removbeal

I have a friend that does watercolours. I want to take her image and remove the background altogether so that I can have a solid white background. Now the lighter version jpg attached, the backgound doesn't look bad but if you check the darker version you can see how bad it really is. Since the image is a watercolour, without clearly defined edges, it there any easier way than to  darken the image and then painstakingly erasing the background?

Bob