Curiously ,in the Nasa image you post, the CSM module show the same size then Collins crater, 3.9mt vs 2.4km, maybe with some trigonometry is possible to calculate the roughly CSM altitude...
Absolutely. Not only is it possible, but it is quite accurate. All we need to accomplish this is data about the image scale, which can be obtained with knowledge of the focal length and the scan size of the raw film. This data can be obtained from the original source.
From this, we see the image was captured with an f/2.8 Zeiss lens, focal length 80mm. Also, we know from reading the documentation of the film scanning process that the scanner used has 5um pixels.
This allows us to calculate the image scale at 12.88"/px. If you download the full sized image, you can then easily measure features. Shown below is a highly reduced representation of the complete film scan, but I downloaded the full sized image, which is over 14,000 pixels across.
I measured Collins crater at approximately 410 pixels in the full sized image, which equates to an angular diameter of 5281", or 1.47 degrees. This same region of the image corresponded to 2.8km across the lunar surface when measured with LROC data. Now, using the simple trigonometric relationship of tan(1.47)=2.8km/X, we can solve for X=109km, which represents the approximate altitude of the spacecraft above the lunar surface. Checking the Apollo flight journal, the reported altitude at time of the decent burn was approximately 60 nautical miles, which is equivalent to 111km, for an error of less than 2% from my estimate.
Further, we can use the diameter of the command module Columbia of 3.9m to determine the approximate separation distance between the CSM and LM. The measured width of the Columbia CSM in the full sized image is 392 pixels, which yields an angular diameter of 5049", or 1.40 degrees (as you point out, very similar in apparent size to Collins crater). Using the relationship tan(1.40)=3.9m/X, we solve for X=159m, which represents the separation distance between the LM and CSM at the time of the image.