Mesh network with high data rate on 868MHz
ZigBee is a mesh network protocol working in the 868MHz band (amongst others), and the only one I know to have reach an acceptable level of maturity.
According to the ZigBee Wikipedia article:


  868 MHz provides a data rate up to 20 kbit/s


At that datarate, transmission of a still image is possible in less than 10 seconds (assuming heavy JPEG compression), but video is not.

The 868 band is limited in size (863 to 870MHz), the RF power is limited to 14dBm and emitters must limit their duty cycle to less than 1%, so this band is really not suited for high datarates application.

Given your constraints, I suggest you switch to the 2.4GHz band, that is much wider (80MHz of usable band), allow more powerful nodes, and does not limit duty cycle. ZigBee 2.4GHz would be a solution, so would a solution based on mesh-WiFi (standard WiFi routers with community-developed firmware running mesh routing protocols such as BATMAN ).