It is just amazing with how much vague generalization this term usually gets applied to visual matter. Beyond explainable, rhythm became a popular term for expression of a whole load of unarticulated feelings about the image - while at the same time, the official definition frugally ends up as "(orderly) repetition of visual elements". Now, the "orderly repeat" is only the simplest form, the lowest level still going as an idea of rhythm. In music (which, in comparison, seems so structurally advanced), this would be called "a tempo", almost derogatively so, like a metronome beat itself. We may just admit an inferiority of the eye here, and let the ear show us the way: the complexity of rhythmic shapes only starts with gradations, alternations, variations and inversions, and goes all the way to those which cannot be analytically subdued to any periodic model. What is important here for the perception of rhythm is the feeling of that mentioned tempo. It seems that the help we need is a sort of coordinate system: this is somewhat a condition (and an integral part) of the rhythm. Which means, if this isn't quite a rhythm: oo   o o oo o   o oo ooo   o  o, then this for sure is: oo...o.o.oo.o...o.oo.ooo...o..o. As capable we are of seeing the surface of the image as a possible coordinate system, that much more open we'll be towards the perception of complex rhythmical forms. The obvious question is just where do we get the coordinate system? Well, where do we get the tempo of music before it starts? No silence, and no white paper have it. We have to wait for the music to start and bring the idea of tempo: at the same moment reading of rhythm begins. The visual elements of the image are the coordinates for themselves, and their own rhythm. This also concludes that the whole idea of tempo is just an intermediate tool, a derivative of rhythm itself - so let's by all means leave the metronome in the practice room. Every visual presence causes the emergence of certain visual rhythm (is there any need at all to take a reserve and limit this to "at least two" elements of any quality?). It is only to be expected for the simpler rhythms to be more available - an easier read. Beside simplicity, one more ingredient makes the rhythm obvious: its dynamic character. The real elements of rhythm are not the actual shapes and colors in image as much as the visual forces these produce. All the composition forces here mentioned are a part of this, which defines the rhythm as a direct product and a manifestation of composition itself. Strong and obvious rhythm is an exhibition of strong forces which, well phased, create an active stream of energy - perceived so clearly that is often taken as the essential axis of composition.
	rhythm
	The rhythm here isn't very obvious, but its appearance is quite interesting. A very static and strong image, anchored by the central mass, gets the first stimulus by the right window "jumping" away from branch on the ground. The sliver of window in the upper right amplifies that movement to the intensively dynamic relation. Only then do we start to go back connecting all the rhythmic elements (similar and not) into almost theatrically ironic mix of the two different image halves, successfully keeping the eye bouncing around like a ping pong ball.