  We present high-resolution HST WFPC2 images of compact nebulosity surrounding
the cool M-type hypergiants NML Cyg, VX Sgr and S Per. The powerful OH/IR
source NML Cyg exhibits a peculiar bean-shaped asymmetric nebula that is
coincident with the distribution of its H2O vapor masers. We show that NML
Cyg's circumstellar envelope is likely shaped by photo-dissociation from the
powerful, nearby association Cyg OB2 inside the Cygnus X superbubble. The OH/IR
sources VX Sgr and S Per have marginally resolved envelopes. S Per's
circumstellar nebula appears elongated in a NE/SW orientation similar to that
for its OH and H2O masers, while VX Sgr is embedded in a spheroidal envelope.
We find no evidence for circumstellar nebulosity around the intermediate-type
hypergiants rho Cas, HR 8752, HR 5171a, nor the normal M-type supergiant mu
Cep. We conclude that there is no evidence for high mass loss events prior to
500-1000 yrs ago for these four stars.
