./scan.py file.jpg 300
Found scanner 'HP LaserJet MFP M28w (4F952B)._uscan._tcp.local.' at 'NPI4F952B.local.'
Scanner information:
<!-- THIS DATA SUBJECT TO DISCLAIMER(S) INCLUDED WITH THE PRODUCT OF ORIGIN. -->
<scan:ScannerCapabilities xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:scan="http://schemas.hp.com/imaging/escl/2011/05/03" xmlns:pwg="http://www.pwg.org/schemas/2010/12/sm" xsi:schemaLocation="http://schemas.hp.com/imaging/escl/2011/05/03 eSCL.xsd">
	<pwg:Version>2.63</pwg:Version>
	<pwg:MakeAndModel>HP LaserJet MFP M28w</pwg:MakeAndModel>
	<pwg:SerialNumber>VNC3C76616</pwg:SerialNumber>
	<scan:UUID>564E4333-4337-3636-3136-84A93E4F952B</scan:UUID>
	<scan:AdminURI>http://NPI4F952B.local.</scan:AdminURI>
	<scan:IconURI>http://NPI4F952B.local./ipp/images/printer.png</scan:IconURI>
	<scan:Platen>
		<scan:PlatenInputCaps>
			<scan:MinWidth>300</scan:MinWidth>
			<scan:MaxWidth>2550</scan:MaxWidth>
			<scan:MinHeight>300</scan:MinHeight>
			<scan:MaxHeight>3508</scan:MaxHeight>
			<scan:MaxScanRegions>1</scan:MaxScanRegions>
			<scan:SettingProfiles>
				<scan:SettingProfile>
					<scan:ColorModes>
						<scan:ColorMode>RGB24</scan:ColorMode>
						<scan:ColorMode>Grayscale8</scan:ColorMode>
					</scan:ColorModes>
					<scan:ContentTypes>
						<pwg:ContentType>Photo</pwg:ContentType>
						<pwg:ContentType>Text</pwg:ContentType>
						<pwg:ContentType>TextAndPhoto</pwg:ContentType>
					</scan:ContentTypes>
					<scan:DocumentFormats>
						<pwg:DocumentFormat>image/jpeg</pwg:DocumentFormat>
						<pwg:DocumentFormat>application/pdf</pwg:DocumentFormat>
						<pwg:DocumentFormat>application/octet-stream</pwg:DocumentFormat>
						<scan:DocumentFormatExt>image/jpeg</scan:DocumentFormatExt>
						<scan:DocumentFormatExt>application/pdf</scan:DocumentFormatExt>
						<scan:DocumentFormatExt>application/octet-stream</scan:DocumentFormatExt>
					</scan:DocumentFormats>
					<scan:SupportedResolutions>
						<scan:DiscreteResolutions>
							<scan:DiscreteResolution>
								<scan:XResolution>200</scan:XResolution>
								<scan:YResolution>200</scan:YResolution>
							</scan:DiscreteResolution>
							<scan:DiscreteResolution>
								<scan:XResolution>300</scan:XResolution>
								<scan:YResolution>300</scan:YResolution>
							</scan:DiscreteResolution>
							<scan:DiscreteResolution>
								<scan:XResolution>600</scan:XResolution>
								<scan:YResolution>600</scan:YResolution>
							</scan:DiscreteResolution>
						</scan:DiscreteResolutions>
					</scan:SupportedResolutions>
					<scan:ColorSpaces>
						<scan:ColorSpace>sRGB</scan:ColorSpace>
					</scan:ColorSpaces>
				</scan:SettingProfile>
			</scan:SettingProfiles>
			<scan:SupportedIntents>
				<scan:Intent>Document</scan:Intent>
				<scan:Intent>Photo</scan:Intent>
				<scan:Intent>Preview</scan:Intent>
				<scan:Intent>TextAndGraphic</scan:Intent>
			</scan:SupportedIntents>
			<scan:MaxOpticalXResolution>600</scan:MaxOpticalXResolution>
			<scan:MaxOpticalYResolution>600</scan:MaxOpticalYResolution>
		</scan:PlatenInputCaps>
	</scan:Platen>
	<scan:eSCLConfigCap>
		<scan:StateSupport>
			<scan:State>disabled</scan:State>
			<scan:State>enabled</scan:State>
		</scan:StateSupport>
		<scan:ScannerAdminCredentialsSupport>true</scan:ScannerAdminCredentialsSupport>
	</scan:eSCLConfigCap>
</scan:ScannerCapabilities>

Our scan request:
<?xml version='1.0' encoding='UTF-8'?>
<scan:ScanSettings xmlns:pwg="http://www.pwg.org/schemas/2010/12/sm" xmlns:scan="http://schemas.hp.com/imaging/escl/2011/05/03">
  <pwg:Version>2.6</pwg:Version>
  <pwg:ScanRegions>
    <pwg:ScanRegion>
      <pwg:XOffset>0</pwg:XOffset>
      <pwg:YOffset>0</pwg:YOffset>
      <pwg:Width>2550</pwg:Width>
      <pwg:Height>3508</pwg:Height>
      <pwg:ContentRegionUnits>escl:ThreeHundredthsOfInches</pwg:ContentRegionUnits>
    </pwg:ScanRegion>
  </pwg:ScanRegions>
  <scan:InputSource>Platen</scan:InputSource>
  <scan:ColorMode>RGB24</scan:ColorMode>
  <scan:XResolution>300</scan:XResolution>
  <scan:YResolution>300</scan:YResolution>
</scan:ScanSettings>

Content-Length: 0
Cache-Control: no-cache, no-store, must-revalidate
Location: http://192.168.100.8:80/eSCL/ScanJobs/kh4djjux-33mz-w8se-1001-wx0r90yf
Server: ApolloLedmServer/1.0
Connection: keep-alive

Scanning to: file.jpg
Traceback (most recent call last):
  File "./scan.py", line 120, in <module>
    data = urllib2.urlopen(req)
  File "/usr/lib/python2.7/urllib2.py", line 154, in urlopen
    return opener.open(url, data, timeout)
  File "/usr/lib/python2.7/urllib2.py", line 435, in open
    response = meth(req, response)
  File "/usr/lib/python2.7/urllib2.py", line 548, in http_response
    'http', request, response, code, msg, hdrs)
  File "/usr/lib/python2.7/urllib2.py", line 473, in error
    return self._call_chain(*args)
  File "/usr/lib/python2.7/urllib2.py", line 407, in _call_chain
    result = func(*args)
  File "/usr/lib/python2.7/urllib2.py", line 556, in http_error_default
    raise HTTPError(req.get_full_url(), code, msg, hdrs, fp)
urllib2.HTTPError: HTTP Error 503: Service Unavailable