Is image description sufficient for alt-text even if hidden?

Site URL: http://tanyaarya.co.uk

I realised after I had uploaded all of my images to my photography portfolio that I should have renamed my image files for SEO. If I choose to add this in as "image description" in my gallery sections instead - will this be sufficient if I choose to hide the caption or do I need to rename all of my files and re-upload?

Any help appreciated! 

Thanks 

Adding image caption is enough😊

@thesimpleexplorer even hidden image captions will be added as alt-text in Squarespace.