Using PyXA, Automator, and PIL to create a mosaic of selected images.

select_photos_for_mosaic.py

import PyXA, math
from PIL import Image

# Execute Automator workflow and receive list of image paths
automator = PyXA.Application("Automator")
workflow = automator.open("/Users/exampleuser/Library/Mobile Documents/com~apple~Automator/Documents/Ask For Photos.workflow")
image_paths = workflow.execute()

# Set base dimensions of mosaic images
base_width = 400
base_height = 200

# Get number of rows and columns
root = int(math.sqrt(len(image_paths)))

# Create empty canvas
dim = (root * base_width, root * base_width)
mosaic = Image.new("RGB", dim)

# Populate the canvas
for row in range(0, root):
    for col in range(0, root):
        # Load image from path
        path = image_paths[row + col * root]
        img = Image.open(path)

        # Resize
        width = int(max(base_width, base_width/img.size[0] * img.size[1]))
        img = img.resize((base_width, width), Image.ANTIALIAS)
        mosaic.paste(img, (base_width * col, base_width * row))

mosaic.show()

select_photos_for_mosaic_bulk_ops.py

# Tested with PyXA 0.1.1
import PyXA, math

# Execute Automator workflow and receive list of image paths
automator = PyXA.Application("Automator")
workflow = automator.open("/Users/exampleuser/Library/Mobile Documents/com~apple~Automator/Documents/Ask For Photos.workflow")
image_paths = workflow.execute()

# Set base dimensions of mosaic images
base_width = 400
base_height = 200

# Get number of rows and columns
root = int(math.sqrt(len(image_paths)))

mosaic = None
for index in range(0, len(image_paths), root):
    row_image = None
    if index + 1 < len(image_paths):
        # Construct rows by stacking images horizontally
        images = PyXA.XAImage.open(image_paths[index], image_paths[index + 1])
        images.resize(base_width, base_height)
        row_image = images.horizontal_stitch()

        # Construct mosaic by stacking rows vertically
        if mosaic is None:
            mosaic = row_image
        else:
            mosaic = PyXA.XAImage.vertical_stitch([row_image, mosaic])

mosaic.show_in_preview()