Raw

Platform: spbctf | Category: Misc | Type: Challenge | Difficulty: Easy | OS: NA | Author: XESXOR | Date: 2026-03-09 | Status: Solved Techniques: autocorrelation_width_detection, image_transformation, raw_image_dimensions_detection

Summary

Task: View a raw24 image file without headers. Solution: Used autocorrelation to detect image width (736x1038), then rotated and flipped the image to read the flag.

Raw - Forensics Kids 2.0

Description

"Кто быстрее посмотрит картинку?" (Who will view the image faster?)

Given file image.raw24.zip containing image.raw24 (2,291,904 bytes).

Analysis

The file is a raw 24-bit RGB image without headers:

• File size: 2,291,904 bytes
• 3 bytes per pixel (RGB) = 763,968 pixels
• Need to determine the correct image dimensions

Autocorrelation was used to determine the image width - a method that finds periodicity in data. The correct width gives maximum correlation between adjacent rows. ‍​‌‌​​‌​​​‌‌​​‌​​​​‌‌​‌​​​​‌‌‌​​‌​​‌‌​​​‌​​‌‌‌​​​​​‌‌​‌‌​​​‌‌​​​​‍

Solution

Step 1: Determining dimensions via autocorrelation

 python read-only • copy allowed Copy
#!/usr/bin/env python3
from PIL import Image
import numpy as np

# Read raw data
with open('image.raw24', 'rb') as f:
    data = f.read()

# 2,291,904 bytes / 3 = 763,968 pixels
total_pixels = len(data) // 3
print(f"Total pixels: {total_pixels}")

# Factorization to find possible dimensions
# 763968 = 2^7 * 3 * 1993 = 736 * 1038
# Autocorrelation showed width 736

width = 736
height = total_pixels // width  # 1038

Step 2: Opening and transforming the image

‍​‌‌​​‌​​​‌‌​​‌​​​​‌‌​‌​​​​‌‌‌​​‌​​‌‌​​​‌​​‌‌‌​​​​​‌‌​‌‌​​​‌‌​​​​‍

 python read-only • copy allowed Copy
#!/usr/bin/env python3
from PIL import Image
import numpy as np

# Read raw data
with open('image.raw24', 'rb') as f:
    data = f.read()

width, height = 736, 1038

# Create image from raw RGB data
img = Image.frombytes('RGB', (width, height), data)

# Image shows an anime character, but text is upside down and mirrored
# Rotate 180 degrees and flip horizontally
img_fixed = img.rotate(180).transpose(Image.FLIP_LEFT_RIGHT)
img_fixed.save('image_fixed.png')

Step 3: Reading the flag

After transformation, the text at the top of the image becomes readable: spbctf{REDACTED} ‍​‌‌​​‌​​​‌‌​​‌​​​​‌‌​‌​​​​‌‌‌​​‌​​‌‌​​​‌​​‌‌‌​​​​​‌‌​‌‌​​​‌‌​​​​‍

The flag hints at tools for viewing raw images:

• GBS - raw image viewer
• GIMP - can open raw data via Import Raw Image Data ‍​‌‌​​‌​​​‌‌​​‌​​​​‌‌​‌​​​​‌‌‌​​‌​​‌‌​​​‌​​‌‌‌​​​​​‌‌​‌‌​​​‌‌​​​​‍