Two things to bear in mind are that the eyes follow a line, and that it also tries to construct a line from appropriate suggestions as clear line provides a natural path for the eye, which moves along it. The more active the line, the stronger the encouragement for the eye to follow it, hence diagonals and curves work better in this way than verticals and horizontals.
• The Art Of Photography (OCA course book), Part 2, Using Lines In Composition, p.81
Part 1: Look at the two provided photographs and find the implied lines by way of indications or arrows.
Part 2: Select three already taken photographs and find the implied lines in each.
Part 3: Take two new photographs that each contain either an eye line or the extension of a line or lines that point.
In this image the strongest implied lines are suggested by the postures of both the man and the bull. The flow of his cape, and the two principal colours in it also give rise to more implied lines, whose direction seems to flow or point inwards to the centre of the image. The implied line suggested by the bull is mostly due to it’s apparent motion or direction of travel, again to the centre of the image.
In this image, the most obvious implied lines are those suggested by the direction in which the man appears to be moving, the eye line of both of the horses (with that being so especially for the horse in the foreground) closest to the man, as well as that of the apparent angle at which the horses appear to be standing or moving at. The strongest line for me is that of the horses postures, as it dominates the image, and is the immediate focus of the eye when first seen. I think the implied lines given by all three subjects makes for a very compact image, and helps to focus attention on the very dynamic quality of the image as a whole.
In this photo the alignment of the bottles gives rise to very many combinations of implied lines, with not all being indicated. The grouping of the bottles as a whole also suggest some directionality, as in pointing upwards.
The implied lines in this photo are much simpler, and maybe not as clear, certainly not as strong as in the previous photo. The line up of the thin poles leading into the lake is principal to the image as a whole, but the boat in the background suggests movement in a certain direction, whether it is actually doing so or not.
The strongest element of the implied lines in this photo is chiefly one of direction. The women all face the same direction, though their slow movement forward may not be so apparent.
The implied lines are are clear as the the arrows of direction. It is natural to extend ones gaze to follow the indications into the distance, especially when presented with a wider view.
Unless you knew what this is, one might not notice or recognise the implied lines in this image, certainly not as readily as in the previous photo. Here the wire mesh dishes of a microwave relay mast imply direction, pointing to where signals are being sent or received from.
It took me a while to get the point of the exercise, despite it being readily described. Maybe I somehow lack the ability to see implied lines in photos, they are not always apparent to me. At least one thing it has taught me is to probe deeper into an image for them, especially when need requires.