import scalebars as sb
import scipy as sp
import matplotlib.pyplot as plt

mydata = sp.rand(200,400)
fig = plt.figure(1)
ax = fig.add_subplot(111)
ax.imshow(mydata, cmap = plt.cm.gray)
sbar = sb.AnchoredScaleBar(ax.transData, 50, "50 u", style = 'bright', loc = 4)
ax.add_artist(sbar)
plt.show()