Is it possible to change the OBS virtual camera offline image?
Yes. (Doing this really isn't necessary.)
Oh, you're asking how to do it?
It's a PNG stored in C:\Program Files (x86)\obs-studio\data\obs-plugins\win-dshow by default, placeholder.png.
I believe it has a resolution limit, a filesize limit and possibly some colorspace requirements, so make sure you just rename it to something else (rather than deleting or overwriting it) so you can refer back to the original in case your replacement image makes OBS crash.
Read up a bit in the thread. I listed the location before.On which Path?
No. 24-bit PNG, possibly with a resolution and filesize limit.and can I use gifs?