Computationally intensive technique to search for TNO's within the noise of historical photographic data?
Dark Energy Survey data have yielded several TNO discoveries.
Bernardinelli et al. 2020 describe their method in detail.
First they compute a trial orbit from images where a transient object was detected. Then

Final validation of the reality of linked orbits uses a new &quot;sub-threshold confirmation&quot; test, wherein we demand the object be detectable in a stack of the exposures in which the orbit indicates an object should be present, but was not individually detected.

Their figure 10 shows a candidate object passing that test; figure 11 shows one failing.
Rice and Laughlin 2021 use a baseline subtraction and shift-stacking technique to search TESS data for TNOs without prior detections.
After verifying that they recover a few known TNOs this way, they list a few unknown candidates for further observation.
If neither of these is what you're thinking of, ADS's References and Citations links may help you find it.