Create a response object with the data and then set the content type header. Set the content disposition header to attachment if you want the browser to save the file instead of displaying it.

@app.route('/images/<int:pid>.jpg')
def get_image(pid):
    image_binary = read_image(pid)
    response = make_response(image_binary)
    response.headers.set('Content-Type', 'image/jpeg')
    response.headers.set(
        'Content-Disposition', 'attachment', filename='%s.jpg' % pid)
    return response

Relevant: werkzeug.Headers and flask.Response

You can pass a file-like object and the header arguments to send_file to let it set up the complete response. Use io.BytesIO for binary data:

return send_file(
    io.BytesIO(image_binary),
    mimetype='image/jpeg',
    as_attachment=True,
    download_name='%s.jpg' % pid)

Prior to Flask 2.0, download_name was called attachment_filename.

What you get is form data and I think you want to receive the uploaded file.
Try request.files and you will get a file-like object of type FileStorage. From this you can read the content of the file with read().

file = request.files['file']
data = file.read()

The objects in request.files are FileStorage objects. They have the same methods as normal file objects in python.

So, to get the contents of the file as binary, just do this:

data = request.files['file'].read()

Then pass that parameter into the INSERT.

You can get the non-form-related data by calling request.get_data() You can get the parsed form data by accessing request.form and request.files.

However, the order in which you access these two will change what is returned from get_data. If you call it first, it will contain the full request body, including the raw form data. If you call it second, it will typically be empty, and form will be populated. If you want consistent behavior, call request.get_data(parse_form_data=True).

You can get the body parsed as JSON by using request.get_json(), but this does not happen automatically like your question suggests.

See the docs on dealing with request data for more information.

JSON does not support binary data directly. JSON supports strings, but they are like unicode strings in Python.

Usually the base64 encoding is used for transferring binary data via JSON.

One possible solution is to use the data URLs:

import flask, io
from base64 import b64encode

@app.route("/map/tileset/prepare", methods=['POST'])
def prepare_tileset():
    # ...

    tiles = []
    for i in range(original.width // width):
        for j in range(original.height // height):
            rect = ((width)*i, (height)*j, (width)*(i+1) - 1, (height)*(j+1) - 1)
            tile = original.crop(rect)

            # BytesIO is an in-memory file abstraction so we don't have
            # to write any actual files to disk
            f = io.BytesIO()
            tile.save(f,"PNG")
            tile_png_bytes = f.getvalue()

            tile_png_b64 = b64encode(tile_png_bytes).decode()
            # remove newlines
            tile_png_b64 = tile_png_b64.replace('\n', '')
            tile_data_url = 'data:image/png;base64,' + tile_png_b64

            tiles.append(tile_data_url)

    return flask.jsonify(tiles)

Not tested, hope it works :)