Using http://docs.python-requests.org/ to access OMERO via json api. For OMERO 5.2.x and earlier. See discussion at https://www.openmicroscopy.org/community/viewtopic.php?f=6&t=8077

webgateway_json.py

import requests
session = requests.Session()

BASE_URL = "https://test.openmicroscopy.org/omero/"
# BASE_URL = "http://localhost:4080/"

login_url = BASE_URL + "webclient/login/"
r = session.get(login_url)
token = r.cookies['csrftoken']
# Add token and referer to session header
session.headers.update({'X-CSRFToken': token,
                        'Referer': login_url})

# Login with username, password and server
payload = {'username': 'will',
           'password': 'ome',
           'server': 1}
r = session.post(login_url, data=payload)

projectId = None
datasetId = None
imageId = None

# list Projects
projects_url = BASE_URL + "webgateway/proj/list/"
r = session.get(projects_url)
projects = r.json()
for p in projects:
    print p['id'], p['name']
    if p['name'] == 'DVs':
        projectId = p['id']

# list Datasets in Project
datasets_url = BASE_URL + "webgateway/proj/%s/children/" % projectId
r = session.get(datasets_url)
datasets = r.json()
for d in datasets:
    if d['name'] == 'dv':
        datasetId = d['id']

# list Images in Dataset
images_url = BASE_URL + "webgateway/dataset/%s/children/" % datasetId
r = session.get(images_url)
images = r.json()
for i in images:
    if i['name'] == 'test.dv':
        imageId = i['id']

# Get image data
image_url = BASE_URL + "webgateway/imgData/%s/" % imageId
r = session.get(image_url)
print r.json()


# Log out
logout_url = BASE_URL + "webclient/logout/"
r = session.post(logout_url)
print 'logout', r.status_code