Create set of random JPGs

Question

Here's the scenario, I want to create a set of random, small jpg's - anywhere between 50 bytes and 8k in size - the actual visual content of the jpeg is irrelevant as long as they're valid. I need to generate a thousand or so, and they all have to be unique - even if they're only different by a single pixel. Can I just write a jpeg header/footer and some random bytes in there? I'm not able to use existing photos or sets of photos from the web.

The second issue is that the set of images has to be different for each run of the program.

I'd prefer to do this in python, as the wrapping scripts are in Python.

I've looked for python code to generate jpg's from scratch, and didn't find anything, so pointers to libraries are just as good.

Answer 1

If the images can be only random noise, so you could generate an array using numpy.random and save them using PIL's Image.save.

This example might be expanded, including ways to avoid a (very unlikely) repetition of patterns:

import numpy
from PIL import Image

for n in range(10):
    a = numpy.random.rand(30,30,3) * 255
    im_out = Image.fromarray(a.astype('uint8')).convert('RGB')
    im_out.save('out%000d.jpg' % n)

These conditions must be met in order to get jpeg images:

1. The array needs to be shaped (m, n, 3) - three colors, R G and B;
2. Each element (each color of each pixel) has to be a byte integer (uint, or unsigned integer with 8 bits), ranging from 0 to 255.

Additionaly, some other way besides pure randomness might be used in order to generate the images in case you don't want pure noise.

Answer 2

If you do not care about the content of a file, you can create valid JPEG using Pillow (PIL.Image.new [0]) this way:

from PIL import Image

width = height = 128
valid_solid_color_jpeg = Image.new(mode='RGB', size=(width, height), color='red')
valid_solid_color_jpeg.save('red_image.jpg')

[0] https://pillow.readthedocs.io/en/latest/reference/Image.html#PIL.Image.new

// EDIT: I thought OP wants to generate valid images and does not care about their content (that's why I suggested solid-color images). Here's a function that generates valid images with random pixels and as a bonus writes random string to the generated image. The only dependency is Pillow, everything else is pure Python.

import random
import uuid

from PIL import Image, ImageDraw    


def generate_random_image(width=128, height=128):
    rand_pixels = [random.randint(0, 255) for _ in range(width * height * 3)]
    rand_pixels_as_bytes = bytes(rand_pixels)
    text_and_filename = str(uuid.uuid4())

    random_image = Image.frombytes('RGB', (width, height), rand_pixels_as_bytes)

    draw_image = ImageDraw.Draw(random_image)
    draw_image.text(xy=(0, 0), text=text_and_filename, fill=(255, 255, 255))
    random_image.save("{file_name}.jpg".format(file_name=text_and_filename))

# Generate 42 random images: 
for _ in range(42):
    generate_random_image()