Can matplotlib add metadata to saved figures?

If you are interested in PDF files, then you can have a look at the matplotlib module matplotlib.backends.backend_pdf. At this link there is a nice example of its usage, which could be "condensed" into the following:

import pylab as pl
import numpy as np
from matplotlib.backends.backend_pdf import PdfPages

pdffig = PdfPages('figure.pdf')

x=np.arange(10)

pl.plot(x)
pl.savefig(pdffig, format="pdf")

metadata = pdffig.infodict()
metadata['Title'] = 'Example'
metadata['Author'] = 'Pluto'
metadata['Subject'] = 'How to add metadata to a PDF file within matplotlib'
metadata['Keywords'] = 'PdfPages example'

pdffig.close()

If you are generating SVG files, you can simply append text as an XML comment at the end of the SVG file. Editors like Inkscape appear to preserve this text, even if you subsequently edit an image.

Here's an example, based on the answer from Hooked:

import pylab as plt
import numpy as np

f = "figure.svg"
X = np.random.random((50,50))
plt.imshow(X)
plt.savefig(f)

open(f, 'a').write("<!-- Here is some invisible metadata. -->\n")

As of matplotlib version 2.1.0, the savefig command accepts the keyword argument metadata. You pass in a dictionary with string key/value pairs to be saved.

This only fully works with the 'agg' backend for PNG files.

For PDF and PS files you can use a pre-defined list of tags.

I don't know of a way using matplotlib, but you can add metadata to png's with PIL:

f = "test.png"
METADATA = {"version":"1.0", "OP":"ihuston"}

# Create a sample image
import pylab as plt
import numpy as np
X = np.random.random((50,50))
plt.imshow(X)
plt.savefig(f)

# Use PIL to save some image metadata
from PIL import Image
from PIL import PngImagePlugin

im = Image.open(f)
meta = PngImagePlugin.PngInfo()

for x in METADATA:
    meta.add_text(x, METADATA[x])
im.save(f, "png", pnginfo=meta)

im2 = Image.open(f)
print im2.info

This gives:

{'version': '1.0', 'OP': 'ihuston'}