Defining an overlay image
Screen capture can also be frustrated by displaying a second image
over the main image. This second image could be some logo or other promotional
image but is best made a GIF. The GIF used could be transparent and better still can be
made to continuously sweep across the image.
The advantage of using ImageSafe to do this is that editing of the
original image isn't necessary and if a GIF is used over a JPEG, the GIF will always
appear with it's original quality and crispness. If you were to edit a JPEG and superimpose
the GIF with an editing program the JPEG quality would degrade and the sharpness of the
GIF will be lost. With ImageSafe the GIF is always pixel-perfect.
Overlay image positioning
The overlay can be positioned in the top-left, bottom-right or center of the main image.
Alternatively the exact pixel co-ordinates of the position can be specified. The
co-ordinate position is reletive to the top-left corner of the main image.
Making the image move
Any overlay image, even an animated GIF can be made to move over the image. The overlay
image always starts at the starting place defined as above and then moves either
from left to right, top to bottom, or top-left to bottom-right repeatedly. By pressing
the "Time" button it's possible to change the timing parameters of the movement. The
parameters that can be changed are:
- The inter-frame delay time specified in milliseconds
- The number of pixels moved after each delay
The overlay image will "wrap around" and will always
be present over the main image.
The ability to move the overlay image over the main image is an excellent obstacle to
someone using screen capture to copy an image. It is also an excellent
way to draw attention to advertising information such as the owner's logo.
Using a double image
With a larger main image and a smaller overlay image large parts of the main image can
still be exposed to screen capture and editing out of the overlay. To better protect
against this the "double image" option places two moving images over
the main image so when one overlay image is leaving, the other is dead center over the
main image.
Previewing
Pressing the preview button will let you see what the image looks like with the overlay
before generating the applet. Before the preview button will work, a main image
must be first selected using the file chooser on the right hand side of the display.