I initially thought it's something like "pacing it out", but after googling it that doesn't seem to be the case.
You have a whole bunch of photos and you post them one a day instead of dumping them all at once.
You may be thinking of "pace yourself":
to try not to do things too quickly so that you have enough energy to be able to complete your task successfully: Pacing yourself and setting achievable goals are the keys to success in this business.
from Cambridge Dictionary
At least in computing, there is
divide and conquer.
divide and conquer
(computing) An algorithm design technique applied to various algorithms, such as quicksort, that solve a problem by splitting it recursively into smaller problems until all of the remaining problems are trivial.
Not an idiomatic phrase but a single word which may work here is: instalments.
Yet another word which may work is: piecemeal.
instalment. (US installment)
2. Any of several parts of something which are published, broadcast, or made public in sequence at intervals.
‘A summary of the story will be published in instalments in NZine.’
ADJECTIVE & ADVERB
Characterized by unsystematic partial measures taken over a period of time.
[as adjective] ‘the village is slowly being killed off by piecemeal development’
[as adverb] ‘many organizations have been built up piecemeal’
Rhetorician wrote in a comment:
You might be thinking of the phrase "to space things out" or "spacing things out," instead of "pacing it [things] out." As in, "I plan to space out my mailings, one a day, over the next six months."
In the software development world, we
iterate on the development of a solution until it satisfies our customers' requirements; but this almost always connotes a feedback loop.
For example, you might iterate the process of posting photos by posting some photos each week, and every week you would adjust which photos are selected based on feedback from the previous week's reviews.
Without feedback, the word I'd consider would be to
trickle the release of the photos.