Deep HST frames of the area around the lensed quasar images of the cluster J1004+4112. The photometric passbands are F160W (left-hand panel) and F555W (right-hand panel), close to the H and V bands, respectively. The frames are approximately 15 arcsec on a side; north is up, east to the left. The frames illustrate the likelihood of the stellar populations of small cluster galaxies overlapping the quasar images and producing a microlensing signal. The yellow circles define the boundary of the measurement of optical depth to microlensing for the dwarf cluster galaxies. The three bright star-like images outside the outer circle are, from the north, images B, A, and C.