Well, that link works in the browser, if you remove the trailing comma.
However, when loading it from the device, the server delivers an empty response:
2014-08-15 18:27:29 NetStreamRequest::Open(1): Opening protocol 'https://' host 'dl.dropboxusercontent.com' port 443 location '/u/54467972/DSCN0425.JPG?nocache=14081524499630'
2014-08-15 18:27:29 NetStreamRequest::Open(1) opened http object id 24
2014-08-15 18:27:30 HTTPCurlObject::Pump() resolving completion status to 0 - apparent empty body (0 headers)
2014-08-15 18:27:30 NetStreamRequest::ProcessHeaders(1) content-type: (null) data expected: 0
2014-08-15 18:27:30 NetStreamRequest::Step(1) done, closing stream (0 of 0 bytes, avail=0) status=0 (ok)
This seems to indicate that for some reason, that server simply closes the connection without sending anything back.
Doing a curl command to load the image directly on the device:
curl "https://dl.dropboxusercontent.com/u/54467972/DSCN0425.JPG?nocache=14081524499630" > /tmp/file
.. results in the error:
curl: (35) error:0D0890A1:asn1 encoding routines:ASN1_verify:unknown message digest algorithm
...which would appear to indicate that the DropBox service is requiring an encryption scheme for HTTPS not supported by the version of SSL used by the chumby. This would require a firmware update to address.