The setting was (a) Foscam IP camera is connected to (b) Raspberry Pi with eth0 wired LAN cable. And (b) the Raspberry Pi is connected to internet via wifi, wlan0.
I wanted to access web port of (a) Foscam IP camera via a port, 80, on (b) Raspberry Pi.
Here is MASQUERADE setting that should be stored in /etc/rc.local. The IP address of (a) Foscam IP camera in this setting is 192.168.1.80.
# Enable ip forwarding
echo 1 > /proc/sys/net/ipv4/ip_forward
# Clear all existing iptables rules
/sbin/iptables -F
/sbin/iptables -t nat -F
/sbin/iptables -t mangle -F
# Create new rules for routing between your wireless and wired connection
/sbin/iptables -t nat -A POSTROUTING -o wlan0 -j MASQUERADE
/sbin/iptables -A FORWARD -i wlan0 -p tcp --dport 80 -d 192.168.1.80 -j ACCEPT
/sbin/iptables -A FORWARD -i wlan0 -o eth0 -m state --state RELATED,ESTABLISHED -j ACCEPT
/sbin/iptables -A FORWARD -i eth0 -o wlan0 -j ACCEPT
/sbin/iptables -t nat -A PREROUTING -i wlan0 -p tcp --dport 80 -j DNAT --to 192.168.1.80
This setting is learned from a website, here.