Here is an abstract Continuous Line Drawing which conceals an image of a dog. Possibly you can see some clues as to where the outline of the dog is. The idea is to carry out an Alternate Overdraw along the line throughout the picture which will produce the image of the dog. Start the overdraw with the arc marked with chevrons.
After I developed Alternate Overdraw in 1970, which enabled me to allocate my colour sequence to continuous line drawings, other possibilities started to occur to me. The first was that you could hide an image of an animal within what looked like a totally abstract continuous line drawing.
See below how the dog finally appears. In fact it looks a bit like Ben, who we have been looking after this week.
The start of the process was to sketch a simple dog outline and then , knowing that the outline had to include many crossing lines, I broke the outline down into short lines or arcs which were at an angle to each other.
Next, I needed to run lines through the dog, from various directions, which used these arcs. For it to work, there had to be an odd number of arcs in each line which went across the dog, between each two outer arcs. This was so that, after completion, when you drew an alternate overdraw across the dog, both arcs on the outline were overdrawn. This would result in all the arcs around the outline being overdrawn, thus forming one loop of overdraw.
Within the body of the dog, several overdraw loops were also formed. Similarly in the background a number of overdrawn loops and inner loops resulted.
Of course, trial and error is involved in connecting up all the loose ends (of the lines running through the dog) to achieve a single continuous line through the whole drawing.
Finally, having completed a continuous line, I needed to check that there were no obvious sections which would indicate that an animal was in there.
I did one more embedded image in 1970 before moving on to other things. This time, instead of making the abstract continuous line from flowing curves with no straight lines, I decided to use mostly straight lines and right angles.
This time I was concealing a steam engine and the Alternate Overdraw result is shown below.
As always with my various styles, I wonder who else may be using them and whether they were in use long ago.