This is one more basic functionality in an Articulate product that has been flagged and requested in these forums for years and there does not seem to be any interest in addressing it.
The very basic ability to add captions/credits to images is available for block types in Images and Galleries, but is not available for any of the items in "Interactions" such as Accordions, Tabs or Flashcards.
Adding a text block below some of these to hold a credit does not work well as it would have to be credits for all tabs/accordion pages/cards at once for any images in the above tab set/accordion etc. Placing credits directly on images in an image editing app adds a lot of extra work, and does not allow linking to licenses.
Using Alt tags for credits or captions is in interesting idea (and caption content would actually be consistent with their purpose for accessibility —not so much for credits) but alt tags are not visible except with a screen reader (or other software?). So, not useful for displaying credits.
Are there any plans in the next update to Rise to add credit/text fields under images in tabs/accordions/flashcards?