Yes the picture I posted wasn't a good example, but the first that came up on google. This is the sort of CB I'm talking about:
The main question I had was does a CB HAVE to rain to be a CB (which nimbus suggests). The answer seems to be "NO". See that cauliflower cloud and go running.
By technical definition, yes. A Cb cloud produces or is capable of producing rain. While the common definition, often outlined on ATP and commercial tests, says that the mature stage of the Cb is marked by the appearance of rain at the surface, the truth is that the rain may never reach the surface.
From an aviation point of view, whether rain reaches the surface or not, a Cb can still present significant hazards beneath the cloud. Virga may appear and not reach the surface, but the virga also represents not only downdraft, but accelerating downdraft, potential microbursts, etc. Hail is a concern. Lightening, and strong winds, also. Embedded, turbulence, hail, and icing are prime concerns. Hail can be ejected far from the column. All the usual hazards.
Your pictures, however,do not indicate Cb cells. They may be cumulus as in your first shot, and may be towering cumulus. (Cu, and TCu). Cumulus clouds indicate unstable air to some degree, and are marked by vertical development. This means you have some element of convection vertically, which means the cloud has energy. You have vertical shear, you have movement, and some element of turbulence.
Before a thundercell reaches a Cb status, it's a building TCu, and the upstarts on the upwind, or upshear side of a cell, even a building cell, can be damaging, and extremely powerful. While doing reasearch in building cells, I've been rolled over and stalled with enough violence to damage onboard equipment...I entered the top of a building cell which didn't even show up on radar several years ago, at night. It stalled rapidly enough we got the stick shaker and pusher in a Learjet 35, rolled us 90 degrees, stripped the guts out of my personal computer (in a padded bag in back), and broke the headset that one of our operators was wearing in back. That was simply a little cumulus building on the upwind or upshear side of a cell.
When you do see the big cloud forming, it may be hard to visualize, but what you're seeing is a signpost of activity. Air is blowing through the cloud. It's constantly being formed and breaking up. Wind is passing through the cell or the cloud from one side to the other. You can't really see it as you see the cloud, it appears to move very slowly, and it might appear to simply exist at the visible limits of the the cloud vapor...but it's much more, and there's much more going on beyond what you can see.
Where you see the crisp, building top, it's still got energy. When it begins to look fluffy and wispy, loses some of it's definition, it's lost it's vertical energy and has "glaciated," or turned to ice. This doesn't mean the cell has lost it's energy; it's still got more to give, but it typically marks the upper limit of vertical development. This doesn't mean that it can't start building again, but it takes more updrafts and more moisture (which may be supercooled, or may freeze and continue to build with energy from below). Any condensation and fallout as the air rises may release latent energy and cause an upsurge, and the storm can take off vertically again.
Rain at the surface may appear to mark the Cb, but there's far more to the Cb, and you may never see the rain. Rest assured it's there somewhere, even if you don't see it. I've done weather research in places (Saudi Arabia, for example) where one might not expect significant weather, and some of the buildups weren't that high, but still produced significant icing (3" of icing on a learjet) with clouds that didn't extend much above 15,000 to 20,000' and had more energy than one might have expected from a small cloud.