Specifications for Server Installations are typically tailored to the needs or your network environment but some good specs for planning would be:
OS: Windows Server 2016 or newer
CPU: Quad core CPU recommended
Memory: 8 GB ram
SQL Server 2016 or newer
Recommend at least RAID 1 protection for database drives
Database disk space can be calculated by the following equation: (15Kb per item) X (number of items per day) X (number of days live) = total db space
Number of days live is the total number of days that you want to retrieve images from the live database instead of pulling from an archive.
Disk space should also consider the size of your backup device.