How do I superimpose an image in the back of a matplotlib plot?

I'm trying to superimpose an image in the back of a matplotlib plot. It is being rendered as HTML in a flask website so I am saving the plot as an image before inserting it. The plot without the background image looks like this:

The code that produces the above output is here:

        fname = 'scatter_averages.png'
        url_full = os.path.join(_path_full, fname)
        image = plt.imread("app/static/images/quantum_grid.jpg")
        if os.path.isfile(url_full):
            os.remove(url_full)
        plt.clf()
        df = self.text_numeric_averages()
        if df is not None:
            plt.figure(figsize=(6, 8))
            fig, ax = plt.subplots()
            df.index += 1
            x, y = df.iloc[:, 2], df.iloc[:, 1]
            ax.plot(x, y, '-o')
            plt.xlabel(df.columns[2])
            plt.ylabel(df.columns[1])
            for i in range(len(df)):
                xyi = df.iloc[i, :].values
                ax.annotate(str(df.index[i]) + " " + xyi[0][:3], (xyi[2], xyi[1]))
            axes = plt.gca()
            y_min, y_max = axes.get_ylim()
            x_min, x_max = axes.get_xlim()
            # ax.imshow(image, extent=[x_min, x_max, y_min, y_max])
            plt.savefig(url_full)

The commented out line above is my attempt to get the image to superimpose. The output when that line is uncommented is this:

How do I keep the sizing and scale of the first image but use the background image in the second plot as the background? I'm not concerned with the image looking distorted.

from How do I superimpose an image in the back of a matplotlib plot?