Hi klosb,
Keyword is an entity to manage images, so you could refer to following workaround and check whether it makes sense for you.
1. Trigger a workflow on creation of File entity, in the process, generate a new keyword record and populate its fields with data from file.

2. Associate keyword and file using Associate Entity method of Dynamics 365 Workflow Tools.
(Set both Relationship Name and Relationship Entity Name to msdyncrm_msdyncrm_keyword_msdyncrm_file)

3. Workflow steps overview

Once we upload an image to Marketing application, it will generate a keyword with same file name and associate it to the uploaded image.(The process takes 10 - 15 seconds to do creation and association.)

In other word, if 10 images have been uploaded, then there will be 10 keywords.
Regards,
Clofly