jmc

Looking at the graph, we can see the line intersects the y-axis at y=1. This is the y-intercept, which is equal to the value of $b$. Now, we need to find the slope of the line. Looking carefully, we can see that for every one unit to the right the line travels, it goes up by two units. For example, starting from the y-intercept at $(0,1)$, the line passes through a lattice point one unit over and two units up from there, at $(1,3)$. The rise over run is then $\frac{2}{1}$, so the slope is 2. The equation of this line is $y=2x+1$. Therefore, $mb=2(1)=\boxed{2}$.