Text CDs usually contain either transcriptions of out-of-print
publications and miscellaneous records, or text written for another
media (such as the text for a book that is still available). Usually
CDs with text allow users to copy and paste sections of the text from
the CD into a word processor or other document. Text on these CDs can
either be entered by hand or converted to text by means of Optical Character
Recognition (OCR) software. Both types of input are subject to error.
Image CDs are created when the producer digitizes an image of a source
(book, microfilm, etc.) and places it on the CD. Since it is impossible
to search a graphic for text, publishers usually also include a text
index (which may have hyperlinks to the image) and some sort of search
engine. Most image CDs allow users to copy an image (i.e. a page) and
paste it into other applications.
Non-genealogy CD producers often have a mixture of
text and graphics, allowing users to view and search textual parts of
the CD, and still view photos, sound and video clips, maps, and so forth.
CDs can further be divided into those which rely on a separate program
for reading and searching the CD, and those which have the viewing software
merged with the material. An example of the former
would be Genealogy.com's Family Archives CDs, which require the use of
the Family Archive Viewer (or Family Tree Maker) to read the CDs; the
latter can be seen in ABC-CLIO's Biography Database. CDs that require
the use of a reader program such as Adobe Acrobat, Folio Bound Views,
or similar programs are almost always included on the CD; the Genealogy.com
Family Archives CDs do not include a viewer on the CDs themselves, but
the viewer is available without charge. Check with the publisher if
you are unsure whether or not a particular CD comes with a viewer.