  We present a novel approach for investigating lens phenomenology of cosmic
strings in order to elaborate detection strategies in galaxy deep field images.
To account for the complexity of the projected energy distribution of string
networks we assume their lens effects to be similar to those of a straight
string carrying a {\em random} lineic energy distribution. In such a model we
show that, unlike the case of uniform strings, critical phenomena naturally
appear. We explore the properties of the critical lines and caustics. In
particular, assuming that the energy coherence length along the string is much
smaller than the observation scale, we succeeded in computing the total length
of critical lines per unit string length and found it to be $4/\sqrt{3} {\bf
E}(3/4)$. The length of the associated caustic lines can also be computed to be
$16/(\pi \sqrt{3}) {\bf E}(3/4)$. The picture we obtain here for the
phenomenology of cosmic string detection is clearly at variance with common
lore.
