While the B-24 was built in larger numbers than any other multi-engine plane in the US arsenal and was factory- and field-modified into many useful configurations, its history and evolution were not nearly so well documented in the contemporary press as its sister, competitor, bomber the B-17.

The examples below are educated guesses in many cases, based on information in Jane's, Hess, et al, and Wikipedia. IDs for specific models are mostly drawn from Joe Baugher's page (http://www.joebaugher.com/usaf_serials/usafserials.html and links), based on tail numbers.
Many wartime photos had some or all of the armament, and often tail numbers or other identifiable features, dodged out; dorsal turret and tail guns were usually shown, however.
It is probably worth noting that none of the photos from my magazines shows the waist guns deployed. So the difference between the open-window, back-to-back deployment of the early models and the glassed-in, staggered deployment of the late models is not obvious — indeed, is not visible in any of these photos, unlike the case with the B-17.

XB-24: The prototype was reconfigured a number of times in development.
An August, 1942, ad shows the rightside nose and inner engine nacelles. Plane is in natural metal finish, has short nose, no "football," no dorsal turret, round (non-turbocharged) engine nacelles, no "rams-horn" pitot tubes.

YB-24/LB-30A Liberator: A photo from a March, 1942, ad shows a plane from 2 o'clock high. Plane has short nose, no tail turret, no dorsal turret, round (non-turbocharged) engine nacelles, RAF markings. This plane has a "football," has "rams-horns" at 3-and-9 o'clock positions on nose immediately aft of greenhouse.

B-24A/Liberator I:

B-24C: Short-run version leading up to the definitive B-24D.

B-24D/PB4Y-1/Liberator B.III: The workhorse model, produced in considerable quantities, and apparently in a variety of configurations:

Armament was one of the areas where visible changes happened most frequently.

B-24E/Liberator IV: Essentially a B-24D built at one of the auxiliary plants — Consolidated Fort Worth, Douglas Tulsa, Ford Willow Run (which supplied kits to the other plants for final assembly.) Because the B-24D was built in such large numbers, there were a number of visible configuration differences, especially considering field mods.
Images include:

B-24H/J/PB4Y-1/Liberator B.VI:

  • An October, 1943, news clip is a detail photo of the Emerson nose turret on a Willow Run plane.
  • A December, 1943, ad shows a B-24H (probably B-24H-1-CF 264438 — the tail number is difficult to read) from 2 o'clock, with a clear picture of the Emerson nose turret.
    The plane appears to retain the tunnel-gun windows (lower aft fuselage).
  • Photo from a December, 1943, ad is a detail photo of the Emerson nose turret.
  • A January, 1944, ad shows B-24H-1-CF 264435 from 2 o'clock high and a detail photo of the Emerson nose turret. Plane has astrodome, "rams-horns" at 10-and-2 positions. It appears to have tunnel-gun windows.
  • A February, 1944, ad shows B-24H-1-FO 27614 from 10 o'clock, Plane has Emerson nose turret, "rams-horns" at 10-and-2 positions, star and bar with red border insigne on fuselage.
  • A May, 1944, ad shows a B-24J from 10 o'clock high. Photo shows dorsal, belly and nose turrets; nose turret appears to be Consolidated A-6 type.
  • An August, 1944, ad shows a PB4Y-1 from 10 o'clock high. Plane has midships astrodome, ERCO bow turret.
  • A November, 1944, ad shows a PB4Y-1 from 11 o'clock low. Plane has ERCO bow turret and appears to have ASV radar installation.

    PB4Y-2 Privateer:

    C-87 Liberator Express: Cargo plane derived from the basic B-24 design, produced on the same production line (Fort Worth) as B-24D (and later models). C-87s were used for cargo, troop transport and VIP transport.

    RY-3 Liberator Express:

    Recognition notes: