It's a background.

And the Python source that created it.

# background-spots.py
# Mike Wilson
# March 21, 1997

output_file = "background-spots"
MagicValue = "P2"
ImageWidth = 100
ImageHeight = 100
MaxGrey = 100
MinGrey = int (0.75 * MaxGrey)
image = {}

import rand, math, string

def draw_spot (x, y, r):
    global image
    for ry in range (r):
	for rx in range (ry,r):
	    distance = int (math.sqrt ((rx * rx) + (ry * ry)))
	    if distance < r:
		for qx,qy in ((+1,+1), (+1,-1), (-1,-1), (-1,+1)):
		    for X,Y in ((x+rx*qx, y+ry*qy), (x+ry*qy, y+rx*qx)):
			if X < 0:
			    X = X + ImageWidth
			elif X >= ImageWidth:
			    X = X - ImageWidth
			if Y < 0:
			    Y = Y + ImageHeight
			elif Y >= ImageHeight:
			    Y = Y - ImageHeight
			image[X,Y] = int ((image[X,Y]
					    + MaxGrey - r
					    + distance) / 2)
	    else:
		break

def main ():
    import os
#    file = open (output_file + ".pgm", "w")
    file = os.popen ("ppmtogif > " + output_file + ".gif", "w")
    file.write (MagicValue + "\n")
    file.write (`ImageWidth` + "\n")
    file.write (`ImageHeight` + "\n")
    file.write (`MaxGrey` + "\n")

    global image
    # initialize dictionary
    for h in range (ImageHeight):
	for w in range (ImageWidth):
	    image[w,h] = MaxGrey

    x_dim = range (ImageWidth)
    y_dim = range (ImageHeight)
    widths = range (MaxGrey - MinGrey)
    count = MinGrey/2
    for i in range (count):
	draw_spot (rand.choice (x_dim),
		   rand.choice (y_dim),
		   rand.choice (widths))

    for h in range (ImageHeight):
	for w in range (ImageWidth):
	    file.write (`image[w,h]` + ' ')
    file.close ()

main ()