In the ever-evolving social media landscape, Instagram has transcended from a mere image-sharing platform to a dynamic space for academic libraries to engage with their communities. Following the increased utilization of this platform, several studies have tried to unravel the interplay between nuanced content aspects and follower engagement, but the results are cursory and contradicting. Aiming to address these shortcomings, we conducted an in-depth analysis of 1681 posts from 120 academic libraries' Instagram profiles worldwide to explore the following: content volume and posting frequency; qualitative content aspects such as post categories, characters length, hashtags usage, emojis frequency, and post types; and possible correlations between these content aspects and follower post interaction rates. Our findings uncovered notable disparities in interaction rates among 14 distinct post categories, with content structure characteristics showing minimal influence on these rates. By shedding light on the association between aspects of content structure and follower interaction, the study contributes to the development and optimization of academic libraries' social media strategy, policy redefinition, staff knowledge and practical skills improvement to manage social media, while also opening new research avenues in Instagram utilization in the academic library context.