Can I add herbarium specimens or museum collections to iNaturalist?

iNaturalist's approach towards advancing biodiversity science and conservation is to focus on supporting an active community using the platform to generate, share, explore and curate data rather than focusing solely on accruing data. So while museum and herbarium collections contain important and useful data, iNaturalist should not be used as a repository for digitizing and sharing historical collections data en masse. 

Please check out GBIF or iDigBio as more appropriate repositories. 

If you have a collection of specimens that you have personally gathered, those would be better candidates for iNaturalist. You can post photos of them to iNaturalist and use the date, time, and location of when/where the specimen was collected from the wild for the observation.