To try to answer your first question, you need to look at the claims in the patent. The first claim is as follows:
A composite lecture video generation system comprising:
device operable to generate a screen capture video, based on display
output being output from a display screen of the mobile device, the
screen capture video including display output corresponding to
a video camera module operable to generate an
audio-visual recording of the display screen, the graphical markings,
and one or more physical objects positioned between the video camera
and the display screen; and
a composite lecture video generator
process the screen capture video to increase a
transparency of one or more white portions of the screen capture
synchronize a timing and an orientation of the processed screen
capture video with a timing and an orientation of the audio-visual
recording, by matching, for each of one or more video frames of the
processed screen capture video, the graphical markings included in the
corresponding video frame of the processed screen capture video with
the graphical markings recorded in a specific video frame of the
audio-visual recording; and
superimpose the synchronized processed
screen capture video over the synchronized audio-visual recording to
generate a composite lecture video, the composite lecture video
including the graphical markings included in the screen capture video
superimposed over the graphical markings recorded in the audio-visual
To infringe on a patent you need to implement each and every step in at least one claim. Claim one specifies the use of a video camera. So for instance if your implementation only uses a digitizer and not video camera, you would be clear of claim 1. Each claim needs to be evaluated in this manner separately.
I don't know how you plan on implementing your overlay. What you need to do is read each of the claims and see if your implementation utilizes each and every step in the claim. You should focus on the independent claims (1, 4, 7, 9, 23 and 30).
As to your second question, that is a business matter and not predictable for me. If your overlay clearly infringes on one or more claim, then you should definitely inquire about licensing as there is no real downside. Some companies are happy to license IP for to non-competitive companies and some aren't.
Lastly, if you are using a software product which already has some sort of overlay functionality, it is entirely possible that it is already licensed and free to be used. In this case I would inquire with the software publisher as to the legal status of the functionality being used.