iNaturalist is a citizen science effort with over 300,000 participants who've shared over 14,000,000 photo-vouchered observations representing over 180,000 distinct organisms. iNaturalist represents one of the fastest growing sources of high-quality biodiversity data for science and conservation.
iNaturalist is a photo sharing social network that in many ways is a lot like Flickr. Unlike Flickr:
1. iNaturalist is a community dedicated to recording and sharing photos of living organisms and discussions tend to focus on species identification.
2. Photos are vetted and become research-quality data for science and conservation.
iNaturalist provides a link to a wizard that makes it easy to link your Flickr account to iNaturalist and create iNaturalist observations from your Flickr photos. Presumably you are here because someone added this link in a comment to one of your Flickr photos.
Clicking on this link will launch a page within Flickr where you can authorize third-party application's (like iNaturalist) to link to your Flickr account.
If you authorize this application, iNaturalist will create a new user account for you linked to your Flickr account. These permissions mean that when you use the iNaturalist website you will be able to access your Flickr photos in order to import them into iNaturalist.
Please be aware that no one else will be able to access your Flickr photos. iNaturalist only needs to ask for these permissions so that you, while using your new iNaturalist account, will be able to access your own photos through iNaturalist.
Once you click 'Authorize', iNaturalist will create an iNaturalist account for you using your Flickr login and icon. From your iNaturalist 'Account' Page you can always unlink your Flickr account at a later date.
Next, the wizard will launch the iNaturalist New Observation form. This form will be preloaded with as much information as it can from your Flickr photo. At the very least, the Flickr photo will be selected, but the date, location, and even the species identification might also be selected depending on the metadata on your Flickr photo. You can alter this information or add any missing information before saving the form.
On iNaturalist, observations record encounters with individual living organisms. Photos provide evidence of what you saw that the iNaturalist community can use to vet your observation. Observations should also include a date, location, and the identification of what you saw.
You can learn more about how to get started with iNaturalist here