When a photographer uploads to stock agencies such as Alamy or Shutterstock, they have 2 options to consider.
Option 1 - Commercial - If the image being uploaded is intended to be used for commercial reasons, to be monetised, sell, promote or advertise a product, then for these reasons, the photographer/contributor needs to have a model release form completed by the model.
this link from Alamy is what is required for the model to complete. https://www.alamy.com/contributors/alamy-model-release-form.pdf
Option 2 - Editorial - These are images that will not be used for any of the above and and only used for illustrated news articles so no logos are required to be removed and models do not need to complete a model release form or even be made aware that their image is being uploaded.
If the photographer/stock photo contributor is using a model even if that model happens to be the photographer him or herself and the image serves no news worthy purpose but can only really be used for commercial reasons, then a model release form needs to be completed by him or her, even if its a selfie.
Each Stock photography website has its own forms to be completed without which, the photos will not be accepted as commercial images.
Therefore, just giving the photographer verbal or written permission is not enough to be a contributor, these forms need to be completed and uploaded to the respected site.