Deepest r-band images for the sample of the nine BH candidates. The location of the objects are indicated by red ellipses, taking into account the positional errors reported in the literature (see Table 1). For the sake of visibility, we mark the position of J1803 and J1828 with red tick marks instead of ellipses, as the positional errors are too small to be resolved. The field of view is 20 × 20 arcsec each.