QGIS python code to use images as point symbols

show_picture.py

"""
Use this method to use images stored in a layer field as path
Ex: show_picture( "picture_path_fieldname" )
Path can be absolute or relative to the project
/!\ Project must be saved before use

author: Michaël Douchin, 3liz
inspired by Nathan Woodrow example : http://nathanw.net/2016/02/04/live-svgs/
"""

import re, tempfile, os, base64
from qgis.core import QgsProject

@qgsfunction(args='auto', group='Custom')
def show_picture(picture, feature, parent):
	
	# SVG content template
	svg = """
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<svg><g>
<image xlink:href="data:image/jpeg;base64,{0}" height="256" width="320" />
</g></svg>
"""

	# Build svg file path
	tempDir = tempfile.gettempdir()
	name = u"%s" % feature.id()
	name+= re.sub(r'\W+', '', picture)
	tPath = os.path.join(
		tempDir,
		"%s.svg" % name
	)

	# Return SVG path if already created before
	if os.path.exists( tPath ):
		return tPath.replace("\\", "/")

	# Get the project folder
	p = QgsProject.instance()
	projectDir, projectName = os.path.split(os.path.abspath('%s' % p.fileName()))

	# Get picture absolute path
	if os.path.exists( picture):
		picturePath = picture
	else:
		picturePath = os.path.normpath(
			os.path.join(projectDir, picture)
		)

	# Build svg file
	if os.path.exists( picturePath ):
		with open(picturePath, "rb") as imageFile:
			data = base64.b64encode(imageFile.read())
			newsvg = svg.format(data).replace('\n','')
	else:
		newsvg = svg.format('').replace('\n','')

	# Add content to svg file
	with open(tPath, 'w') as f:
		f.write(newsvg)

	# Return SVG path
	return tPath.replace("\\", "/")