I don′nt know, if we understood each other.
I send screen.
Clean instalation blocksy, imported one starter site. Suplemented caption ( screen 1 )
Expected view after the click onto the picture ( screen 2) – text isn′t able anyvhere, also not in source code.
Many themes support it, so from the point of viev of SEO, it would by good to add it.`
scr1
scr2