This is a classic example of the sort of things "alterationists" cling on to.
Below is the frame in question - Z152
One is a Lightbox frame taken from here - https://sites.google.com/site/lightboxzframes/lightbox-frame-sets
One is a Costella frame taken from here - https://www.assassinationresearch.com/zfilm/
It can be seen the "compression artifacts" apparent in the Lightbox frame are not present in the Costella frame.

The Lightbox site states the following:
The “Lightbox” frames (1280 x 720) have notable compression artifacts.
It is always preferable to use the best available frames when making any analysis of the Z-film.
Hi Dan, I do not know who wrote this. I knew there were four missing frames from the Zapruder film. It looks like there are between 6 and 9. My best guess is that the 7 missing frames from the Tina Towner film took out the wide turn that SSA William Greer made by mistake. My best guess for the missing Zapruder frames is to take out the stop that SSA William Greer made that is probably best witnessed in the Marie Muchmore film. I guess you cannot see it, but in Gerda's gif of Clint Hill, the Nix film and the Zapruder film do not match! Thank you for everything! Sincerely yours, Michael
Missing and Out of Sequence frames in the Zapruder Film
I used two computer based versions of the Zapruder film to do my comparison. The first one is "JFK Assassination, A Visual Investigation" by MacMillian Digital USA. The Second version I used is "Image of an Assassination, A New Look at the Zapruder Film" by MPI Home Video. Here are the results:
Visual Investigation
New Look
1 to 154
Same
1 to 154
155 (misnumbered)*
Equals
157 (correct)*
156 to 157
Equals Missing
155 to 156
158 to 207
Same
158 to 207
208 to 211
Both Missing
208 to 211
212* to 330
Same
212* to 330
331 (correct)
Equals
332 (out of sequence)
332 (correct)
Equals
331 (out of sequence)
333 to 340
Same
333 to 340
341 (correct) Missing
342 to 349
Equals
341 to 348
350 (correct) Missing
351 to 485
Equals
349 to 483
486 (not numbered) Missing
* Note 1: Frame 157 is a splice. The top 1/3 is frame 155 and the bottom 2/3 is frame 157.
*Note 2: Frame 212 is a splice also. The top portion is frame 208 and the bottom portion is 212.
There are a Total of 9 frames missing from "Image of an Assassination, A New Look at the Zapruder Film". There are only 6 frames missing from the "JFK Assassination, A Visual Investigation" versision of the film.
As I watched my copy of the MPI version on DVD, I noticed some white letters kept flashing on the left of the film in the sprocket hole area at regular intervals. Upon closer examination I found that the letters spelled out "KODACHROME II" and "SAFETY FILM". There are also a couple of numbers and symbols between these two phrases which have no meaning to me.
I decided to find out if this message was at a regular interval such that I could determine if any additional frames were missing. The entire message "KODACHROME II ... SAFETY FILM" is between 17 and 18 frames long. The message is flashed 7 times through the Zapruder film. The message can be seen from frames 25 to 41, 92 to 109, 157 to 173, 224 to 241, 288 to 305, 354 to 370 and 418 to 435. The start of the message does not begin exactly in the same place each time in relation to the sprocket holes.
My next step was to measure the distance between each repeating message. After adding in frame 341 & 350 and assuming that 155, 156 & 208 to 211 were the only missing frames, I measured the partial distance that the message took up at the beginning and ending of the phrase. The distance between the 1st & 2nd is 50 5/8 frames; 2nd & 3rd is 48; 3rd & 4th is 50 5/8; 4th & 5th is 47 7/8; 5th & 6th is 50 5/8; and the 6th & 7th is 48. I believe these measurements are close enough to show a pattern: 51; 48; 51; 48; 51; 48. If any 1 or more frames are either added or subtracted then the whole pattern is thrown off. I believe this pattern proves the Zapruder film is "authentic" in that there are only 9 frames missing!
