That empty corner is already working.
Before filling a gap, decide what the extra element would help someone understand.
An empty corner can make a perfectly sensible person reach for another caption. Or a line. Perhaps a tiny label saying exactly what the photograph already says.
Sometimes the space was doing a better job. It separated two ideas, gave the subject room or made a small detail easier to notice. Filling it changes the hierarchy, even when the new addition looks harmless on its own.
Decide what leads
Choose the first thing the composition should make visible. A material detail needs a different crop from a silhouette. A headline may need to lead before the image makes sense.
Then look at what competes with that choice. Two strong elements can become clearer when their scale changes or they move apart. Adding a third rarely settles the argument.
Remove the decorative element in question and compare the two versions. If the reader loses useful information, it has a reason to return. If the design merely looks less busy, it can stay out.
Sparse still needs specific
A layout with very little in it exposes every remaining decision. The crop needs to be deliberate. Type must relate to the subject. A beautiful colour cannot supply the idea on everyone else's behalf.
For a product chosen because of its texture, give the lighting and image scale enough room to show that texture. If the most noticeable thing is the decorative frame, the composition is advertising its own effort.
This is also why removing almost everything can produce an anonymous result. The aim is to make the subject clearer. Emptiness is no substitute for choosing one.
Keep the useful words
A caption that explains an unfamiliar object belongs on the page. So does information needed to use a service. Restraint becomes unhelpful when visitors have to guess what is being offered.
Check the composition with its final copy, especially on a phone. Move supporting information if it needs more room. Keep the gap when it helps the important parts read clearly. There is no prize for filling the canvas.
