How to draw bold/italic text with PIL? ImageFont.truetype(file, size) has an option to specify font size only.
A rather hacky solution to make a font bold if (for whatever reason) you don't have a separate bold version of the font is to print the same text several times with a slight offset.
andaleMono = ImageFont.truetype(ANDALE_MONO_PATH,16)
text = "hello world"
mainOffset = (50,50)
xoff, yoff = mainOffset
draw.text(mainOffset,text,font=andaleMono,fill='black')
draw.text((xoff+1,yoff+1),text,font=andaleMono,fill='black')
draw.text((xoff-1,yoff-1),text,font=andaleMono,fill='black')