Regarding video feeds
You could also try with other browsers :
- sailfish native WebPirate (uses QtWebKit instead of Fennec like the original Browser by Jolla)
- FireFox Android works on Sailfish
- Google Chrome works on Sailfish (and is a different flavor of WebKit than Opera).

I am strongly suspecting that your connected cam doesn't use a standrad video system correctly (e.g.: it's not an HTML5 video tag fed off rtsp), but some weird buggy contraption (e.g.: abusing http in non-conformat ways) that they haven't thoroughly tested everywhere.

Hence my peculiar recommendation (a standard Webkit native app, and then android app which are basically pocket version of the 2 desktop application most likely to have been tested).

If that cam was only tested with internet explorer or with edge, or if it only works with flash or java plugins, you're basically screwed.


Regarding the JPEG :
they are not exactly "downloaded into the gallery".
E-mail attachement are downloaded into "${HOME}/Downloads/mail_attachments/", Picture taken with the Camera are stored inside "${HOME}/Pictures/Camera/" or even on the SDcard, depending on settings.
They just all "show up" in an unified gallery due to how file indexing works in sailfish.
(But you'll need to navigate to a different directory using your favorite files management app)

Mobile phone applications (not only Sailfish OS, but also older OSes like webOS and PalmOS) tend to NOT download attachements automatically to save space on the device and bandwidth on the data plan.

You can change the behaviour in app "Settings" -> bottom tab "Apps" -> icon "Email" -> toggle "Download images automatically".