One reader asked for plug-ins that would generate a random grid over top of an image. Author of Photoshop For Right Brainers and Plug-ins expert Al Ward provides us with this tutorial to solve the problem...
For plug-ins that will help achieve this effect, I'll have to defer to others in that regard. The effect itself is actually a fairly easy thing to achieve without plugins: I'll try to describe the process I came up with as best I can.
1) Open your image.
2) create a new layer
3) We'll tackle the horizontal dividers for the grid first.
First, make the rulers visible and set them to inches. That is a personal preference, so if something else works for you then go for it.
4) select the Single Row Marquee Tool.
Figure out roughly how high you want a single square to be, then measure down the ruler and click on what would be the edge of the first line of rectangles. Fill that selection with Black.
5) Create a new layer, measure down again (it need not be exact... I'll show you why in a bit) and create a new line as described above in the new layer.
6) coninute making layers and lines in each until you have the number of horizontal lines you want, or the entire image has rougly distributed horizontal lines.
7) This part is key: getting the lines to be equadistant. To do this, link all the line layers.
To do this, link all the line layers. Select All (Command/Control+A).
With the line layers linked and the entire document selected, go to Layer>Distribute Linked>Vertical Centers. This will distribute all the lines, top to bottom, equally across the document.
Once done, merge all those line layers together.
8) Repeat the process for the vertical lines. When ready to disribute the lines, Select Distribute Linked>Horizontal Centers.
9) Merbe all the line layers together.
Once the grid is in place, create a new layer.
Grab the Magic Wand tool and, in the grid layer, just click in several random squares. Go to the blank layer and fill the selections with White, Normal, 35% opacity. Select a few more squares, return to the fill layer, and fill those sqares with white, 70% opacity or so (I'll leave the ammount of white in your squares up to you). Just keep doing that... your effect will unfold before your eyes.
When done, simply delete the grid layer. With this process, going into it for the first time and simply looking at the image you provided, the entire image I used was covered with equal squares of varying white in about 4-5 minutes. Not as fast as a filter might allow, but I'm an advocate for knowing how a technique is produced.
I hope this helps. If you need further instruction, i could certainly create a tutorial demonstrating the technique.