Thumbnail creation

4chan uses PHP to generate their thumbnails (and run their site).
PHP uses their own libgd (image processing library) which also uses their own libjpeg-8d.

Media Characteristics

Before 2017, thumbnails used the same jpeg quality: 60.
Since the start of 2017 and beyond, OP thumbnails use 50 and reply thumbnails use 40 as their jpeg image quality scale.

OP Thumbnails

• Max width: 250
• Max height: 250
• JPG quality: 50

Reply Thumbnails

• Max width: 125
• Max height: 125
• JPG quality: 40

Application

To generate checksum-compliant thumbnails you have the following options:

• Use PHP v5.4.15 or later to run the PHP script
• Download the latest pre-built binaries
• Manually build from source

PHP

$ php tg.php
Generate thumbnails from 4chan
tg.php  <input-file>  <output-file>  [reply?1:0]  [sfw-board?1:0]

$ php tg.php img/op.jpg op-new.jpg 0
$ b3sum img/op-thumb-orig.jpg op-new.jpg
e039f64581ee448e8230146272621b4cc9891d1901f42359b66a76c0ee17916b  img/op-thumb-orig.jpg
e039f64581ee448e8230146272621b4cc9891d1901f42359b66a76c0ee17916b  thumb/ops.jpg

$ php tg.php img/reply.jpg reply-new.jpg
$ b3sum img/reply-thumb-orig.jpg reply-new.jpg
7715bcfa13d8bf5597daf7c51caf1dd4ebececce345829bc9700f1f321b4db93  img/reply-thumb-orig.jpg
7715bcfa13d8bf5597daf7c51caf1dd4ebececce345829bc9700f1f321b4db93  reply-new.jpg

$ php tg.php img/alpha-new.jpg 0
$ b3sum img/alpha-thumb-orig.jpg alpha-new.jpg
59ddd640d38aa3f9e40ff81e35755877d2fa4b2f9371ac86572452e85f204701  img/alpha-thumb-orig.jpg
59ddd640d38aa3f9e40ff81e35755877d2fa4b2f9371ac86572452e85f204701  alpha-new.jpg

$ php tg.php img/dance.gif dance-new.jpg 1 0
$ b3sum img/dance-thumb-orig.jpg dance-new.jpg
4270149933bcb5d5cac3bb5934c4422249b38e73c3347ee5f8377d8235cb0c3f  img/dance-thumb-orig.jpg
4270149933bcb5d5cac3bb5934c4422249b38e73c3347ee5f8377d8235cb0c3f  dance-new.jpg

C binary executable

$ ./tg
Generate thumbnails from 4chan
./tg  <input-file>  <output-file>  [reply?1:0]  [sfw-board?1:0]

$ ./tg img/op.jpg op-new.jpg 0
$ b3sum img/op-thumb-orig.jpg op-new.jpg
e039f64581ee448e8230146272621b4cc9891d1901f42359b66a76c0ee17916b  img/op-thumb-orig.jpg
e039f64581ee448e8230146272621b4cc9891d1901f42359b66a76c0ee17916b  op-new.jpg

$ ./tg img/reply.jpg reply-new.jpg
$ b3sum img/reply-thumb-orig.jpg reply-new.jpg
7715bcfa13d8bf5597daf7c51caf1dd4ebececce345829bc9700f1f321b4db93  img/reply-thumb-orig.jpg
7715bcfa13d8bf5597daf7c51caf1dd4ebececce345829bc9700f1f321b4db93  reply-new.jpg

$ ./tg img/alpha.png alpha-new.jpg 0
$ b3sum img/alpha-thumb-orig.jpg alpha-new.jpg
59ddd640d38aa3f9e40ff81e35755877d2fa4b2f9371ac86572452e85f204701  img/alpha-thumb-orig.jpg
59ddd640d38aa3f9e40ff81e35755877d2fa4b2f9371ac86572452e85f204701  alpha-new.jpg

$ ./tg img/dance.gif dance-new.jpg 1 0
$ b3sum img/dance-thumb-orig.jpg dance-new.jpg
4270149933bcb5d5cac3bb5934c4422249b38e73c3347ee5f8377d8235cb0c3f  img/dance-thumb-orig.jpg
4270149933bcb5d5cac3bb5934c4422249b38e73c3347ee5f8377d8235cb0c3f  dance-new.jpg

Checking image information

Imagemagick:
_{(Note: Installing Imagemagick also installs libjpeg and could mess with your libjpeg-8d installation. In that scenario, use the --prefix= flag when building libjpeg-8d)}

identify -verbose -features 1 -moments -unique 1583219690557s.jpg > thumb.txt

Building from source

^{(Iɴsᴛʀᴜᴄᴛɪᴏɴs ᴄᴜʀʀᴇɴᴛʟʏ ᴏɴʟʏ ғᴏʀ Lɪɴᴜx)}

Sources:

• libzlib (optional)
• libpng-1.2.50 (optional)
• libjpeg-8d^[1]
• php5
• koio

Build libzlib

$ cd zlib-1.2.11
$ ./configure --prefix=$(pwd)/build --static --64
$ make
$ sudo make install # Install to prefix
$ export ZLIB_DIR=$(pwd)/build

Build libpng

$ cd libpng-1.2.50
$ cp scripts/makefile.linux Makefile # Then edit the Makefile and change the prefix to $(pwd)/build
$ make
$ sudo make install # Install to prefix
$ mkdir -p build/include build/lib
$ export PNG_DIR=$(pwd)/build
$ cp *.h $PNG_DIR/include
$ cp *.a *.so $PNG_DIR/lib

Build libjpeg

$ cd libjpeg-8d
$ ./configure --prefix=$(pwd)/build --enable-static
$ make
$ sudo make install # Install to prefix
$ export JPEG_DIR=$(pwd)/build

Build php5

$ cd php-5.4.15
$ ./buildconf --force

# If the configure below doesn't work try
# 	autoreconf -fi
# or
# 	aclocal; libtoolize --force; autoheader; autoconf
# and run configure again

$ CFLAGS="-I$ZLIB_DIR/include -I$PNG_DIR/include -I$JPEG_DIR/include" LDFLAGS="-L$ZLIB_DIR/lib -L$PNG_DIR/lib -L$JPEG_DIR/lib" ./configure --prefix=$(pwd)/dist --with-zlib=$ZLIB_DIR --with-zlib-dir=$ZLIB_DIR  --with-png-dir=$PNG_DIR --with-jpeg-dir=$JPEG_DIR --disable-all --disable-libxml --disable-dom --disable-simplexml --disable-xml --disable-xmlreader --disable-xmlwriter --without-pear --without-iconv --enable-debug --enable-cli --with-gd --enable-static --enable-embed=static

# For static builds: --enable-static --enable-embed=static

$ make -j 4
$ make install -j 4
$ export PHP_DIR=$(pwd)/build

Build koio

$ meson setup build --prefix=/ --buildtype=release --default-library=both
$ ninja -C build
$ DESTDIR=../dist/ ninja -C build install
$ export KOIO_DIR=$(pwd)/dist
# Then fix the library folders in dist/lib

Compilation

Finally. Let's compile our program.

minify the php script then run koio ^{(yes you have to build this too)} to generate a c source file that embeds the script

$ koio -o asset.c tg.php://tg.php

$ cc -o tg tg.c asset.c -lphp5 -lpng -ljpeg -lz -lkoio -static

# Or if you installed the libs locally
$ cc -o tg tg.c asset.c -I$PHP_DIR/include -I$PHP_DIR/include/php -I$PHP_DIR/include/php/include -I$PHP_DIR/include/php/main -I$PHP_DIR/include/php/Zend -I$PHP_DIR/include/php/TSRM -I$PHP_DIR/include/php/main/streams -I$ZLIB_DIR/include -I$PNG_DIR/include -I$JPEG_DIR/include -L$ZLIB_DIR/lib -L$PNG_DIR/lib -L$JPEG_DIR/lib -L$PHP_DIR/lib -I$KOIO_DIR/include -L$KOIO_DIR/lib -lphp5 -lpng -ljpeg -lz -lkoio -static

---

How does it work?

PHP is built and statically linked against musl. Using the Zend (PHP's core engine) API in our C code allows us to run an identical VM that made the original thumbnails.

But that's basically just the PHP CLI then?!

This is statically linked, and smaller, hence portable. Furthermore, it has one clear purpose, rather than being a general script runner/interpreter. You could say the PHP script was packaged into a single binary.

How did you do it?

I looked at the Futaba's source code which 4chan is based from + the 4chan source code leak and used the same code they used to generate thumbnails. After finding out which PHP version (5.4.15) was used, I ran php --re gd | grep GD to get the libgd version (2.0.35) and php --ri gd to get the libjpeg (8d) & libpng (1.2.50) versions.

Resources

• PHP5 archives
• Building PHP for Windows
• php-sdk archives
• PHP Windows archives