Virtualbox is a excellent freeware to test Virtual Machine Systems or Virtualisation..  it has a few issues.

It cannot use the builtin Camera iSight or FaceTime HD.. the following is a fix to it.

1. Read Section 9.7 “Webcam passthrough”

2. Note: The webcam passthrough module is shipped as part of the Oracle VM VirtualBox extension pack, which must be installed separately. See Section 1.5, “Installing VirtualBox and extension packs” for more information.

3. Open “terminal” and check which camera you have and then attach it to the VM

find which camera is available on the laptop.
> VBoxManage list webcams
# -- the following is the output
Video Input Devices: 1
.1 "FaceTime HD Camera"
CC243852584F6VVD1
# -- expected output
# alias "user friendly name"
# host path or identifier
#Note: OS X Yosemite does not provide host path..

# if you want to see which camera is used by VirtualBox then
>VBoxManage controlvm "VM name" webcam list
# -- where the "VM name" is the name given by you.. if you cannot remember then
> VBoxManage list vms
"Win7 Ultimate" {4e10f9fa-7eea-4583-b1f9-3f46cd132f28}
"Ubunto 14.04 x64" {a9a7f57c-11b3-48a1-b2bf-b01d498744d2}

# Now that we know that we have webcam "Alias"->.1 and the "VM name"->"Win7 Ultimate" we can now get webcam to work in VBox.
# the Manual in section 9.7 https://www.virtualbox.org/manual/ch09.html#webcam-passthrough
># VBoxManage controlvm "VM name" webcam attach [host_path|alias [settings]]
># VBoxManage controlvm "VM name" webcam detach [host_path|alias]

> VBoxManage controlvm "Win7 Ultimate" webcam attach .1
check if its connected.
>VBoxManage controlvm "Win7 Ultimate" webcam list

# to detach 
> VBoxManage controlvm "Win7 Ultimate" webcam detach .1
check if its disconnected.
>VBoxManage controlvm "Win7 Ultimate" webcam list

on macbook or “Mac OS X Host” there are a few issues
> When the webcam device is detached from the host, the emulated webcam device remains attached to the guest and must be manually detached using the VBoxManage controlvm “VM name” webcam detach … command.<

>Note
1> Be careful with USB devices that are currently in use on the host! For example, if you allow your guest to connect to your USB hard disk that is currently mounted on the host, when the guest is activated, it will be disconnected from the host without a proper shutdown. This may cause data loss.<
2> The EHCI controller is shipped as a VirtualBox extension package, which must be installed separately. See Section 1.5, “Installing VirtualBox and extension packs” for more information.<

for people wanting VirtualBox, a very easy tutorial is here