The designation of a source as "original" or "derivative" depends solely on the form of the record itself, independent of any information contained within the record. An original source is a source that has not already appeared in its given form, whereas a derivative source is one that owes its form to an earlier existing record.
For example, the recorded "deed book" copy of a land record would be considered a derivative source, because the record originally appeared as an earlier handwritten deed that remained in the possession of the land owner after the clerk copied it into the deed book. On the other hand, a tombstone would be considered an original source, because the information has not previously appeared in this form. Published abstracts of wills, digital images of census records, and tombstone photographs or rubbings are all considered derivative sources, while their earliest forms would be original sources.
More important than the source type to the analysis of a record is the information type. As previously mentioned, a record can contain both "primary" and "secondary" information. The difference between these two types lies in the degree of involvement of the informant.
The informant of any record is the person who provided the information. In some records, the informant is explicitly identified by their signature. In others it may be possible to infer the identity of the informant, or it may be impossible to identify the informant at all.
"Primary information" is that information provided by a participant in or eyewitness to the event being reported. "Secondary information" is that provided by an informant who learned of the event from a prior source. If one cannot discern who provided it, then one cannot determine whether the information in the record is primary or secondary.
A death certificate provides a perfect example illustrating the difference between primary and secondary information. Quite a lot of information appears on most death certificates, including the date and place of death, the date and place of birth, and the names of the decedent's parents. Most death certificates also identify the name of the informant. Suppose that your ancestor's death certificate provides all of this information, and his son served as the informant. The son may have witnessed his father's death, so the information regarding this event would be considered primary. He could not, however, have witnessed his father's birth, so this would be considered secondary information. The informant, the son, could only have learned of his father's date of birth, and the identification of his grandparents as his father's parents, from another party who may have been involved—possibly his father or grandparents themselves.
Because of its focus on specific people and everyday events, the burden of proof in genealogy must be much stricter that many other academic fields that deal in abstracts and generalities. For this reason, genealogists must take note of the form of each record as well as the source of information.