  We have isolated a sample of 14 candidate variable objects with extended
image structure to Bj = 22.5 in 0.284 deg^2 of Selected Area 57. The majority
of candidates are blue (U-B<0) and relatively compact. At fainter magnitudes,
there is a steep rise in the number of variable objects. These objects are also
compact and blue, and some of them are likely to be truly stellar. Twelve of
the Bj <= 22.5 candidates have been observed spectroscopically over limited
ranges of wavelength and a variety of resulting signal-to-noise. Five
candidates display spectra consistent with Seyfert-like activity. In most cases
where we have not been able to confirm a Seyfert spectroscopic type, the
spectra are of insufficient quality or coverage to rule out such a
classification. The majority of candidates have luminosities less than 10% of
the nominal demarkation between QSOs and AGN (M(B) = -23). The surface density
of confirmed M(B) > -23 AGN to Bj = 22, including stellar sources, is
~40/deg^2, in good agreement with other surveys at this depth. The confirmed
AGN in extended sources make up 36% of this population. Thus, the application
of a variability criterion to images with extended structure enhances the
completeness of the census of active nuclei. If the majority of our candidates
are bona fide AGN, the surface density could be as high as 82/deg^2 for M(B) >
-23, and 162/deg^2 for all luminosities to Bj = 22, with extended sources
contributing up to 33% of the total. (abridged)
