Darwin Core Issue 68: http://goo.gl/Q7TRn
This term has undergone extensive public commentary since January 2010 when it was first proposed. I will do my best to summarize the thinking on these issues, but please see the full corpus of discussions on tdwg-content to see the full history.
It has been suggested that DigitalStillImage is not necessary as a Darwin Core Type vocabulary term (one of the controlled vocabulary terms for basisOfRecord) for at least two reasons:
1) Dublic Core comments on StillImage (http://dublincore.org/documents/dcmi-type-vocabulary/) as: "Note that Image may include both electronic and physical representations."
2) The basisOfRecord term has no real purpose and without it, there was no need for DigitalStillImage as one of its controlled values.
The context for the second statement was the use of Darwin Core in RDF. The basisOfRecord term is essential in data sharing mechanisms such as in Simple Darwin Core text files or Darwin Core Archives where there is no other way to express what is the fundamental concept for a record.
The impetus for proposing DigitalStillImage was to allow the basisOfRecord to show that the evidence for an Occurrence was based on a digital image (similar to a PreservedSpecimen being evidence). This purpose still has merit.
Discussions on DigitalStillImage touched on many other issues related to ontology and missing or inferred Classes in the Darwin Core. To achieve the original goal behind DigitalStillImage for RDF is more complicated and involves the idea of a Class to represent a concept that could be described as "Evidence". I will create a separate thread for the continuation of that discussion, reserving this thread for the closure of the issue of having no way currently to express that a digital image is the basis for a Darwin Core resource.
To achieve the original goal for the case of non-RDF data sharing mechanisms, I propose that StillImage be added to the list of recommendations for the Darwin Core Type Vocabulary, along with MovingImage and Sound. Doing so will create no backward incompatibilities in the Darwin Core.