How do you base-64 encode a PNG image for use in a data-uri in a CSS file?

I want to base-64 encode a PNG file, to include it in a data:url in my stylesheet. How can I do that?

I’m on a Mac, so something on the Unix command line would work great. A Python-based solution would also be grand.

This should do it in Python:

import base64
encoded = base64.b64encode(open("filename.png", "rb").read())

In python3, base64.b64encode returns a bytes instance, so it's necessary to call decode to get a str, if you are working with unicode text.

# Image data from [Wikipedia][1]
>>>image_data = b'\x89PNG\r\n\x1a\n\x00\x00\x00\rIHDR\x00\x00\x00\x05\x00\x00\x00\x05\x08\x06\x00\x00\x00\x8do&\xe5\x00\x00\x00\x1cIDAT\x08\xd7c\xf8\xff\xff?\xc3\x7f\x06 \x05\xc3 \x12\x84\xd01\xf1\x82X\xcd\x04\x00\x0e\xf55\xcb\xd1\x8e\x0e\x1f\x00\x00\x00\x00IEND\xaeB`\x82'

# String representation of bytes object includes leading "b" and quotes,  
# making the uri invalid.
>>> encoded = base64.b64encode(image_data) # Creates a bytes object
>>> 'data:image/png;base64,{}'.format(encoded)
"data:image/png;base64,b'iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg=='"


# Calling .decode() gets us the right representation
>>> encoded = base64.b64encode(image_data).decode('ascii')
>>> 'data:image/png;base64,{}'.format(encoded)
'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg=='

If you are working with bytes directly, you can use the output of base64.b64encode without further decoding.

>>> encoded = base64.b64encode(image_data)
>>> b'data:image/png;base64,' + encoded
b'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg=='

import base64

def image_to_data_url(filename):
    ext = filename.split('.')[-1]
	prefix = f'data:image/{ext};base64,'
	with open(filename, 'rb') as f:
        img = f.read()
	return prefix + base64.b64encode(img).decode('utf-8')

This should do it in Unix:

b64encode filename.png X | sed '1d;$d' | tr -d '\n' > b64encoded.png

The encoded image produced by b64encode includes a header and footer and no line longer than 76 characters. This format is typical in SMTP communications.

To make the encoded image embeddable in HTML/CSS, the sed and tr commands remove the header/footer (first & last lines) and all newlines, respectively.

Then just simply use the long encoded string in HTML

<img src="data:image/png;base64,ENCODED_PNG">

or in CSS

url(data:image/png;base64,ENCODED_PNG)

b64encode is not installed by default in some distros (@Clint Pachl's answer), but python is.

So, just use:

python -mbase64 image.jpeg | tr -d '\n' > b64encoded.txt

In order to get base64 encoded image from the command line.

The remaining steps were already answered by @Clint Pachl (https://stackoverflow.com/a/20467682/1522342)

This should work in Python3:

from io import BytesIO
import requests, base64

def encode_image(image_url):
    buffered = BytesIO(requests.get(image_url).content)
    image_base64 = base64.b64encode(buffered.getvalue())
    return b'data:image/png;base64,'+image_base64

Call decode to get str as in python3 base64.b64encode returns a bytes instance.

And just for the record, if you want to do it in Node.js instead:

const fs = require('fs');
const base64encodedString = fs.readFileSync('image_file.jpg', {encoding:'base64'});