Pentagonal shaped cap badge ?

[MrsG]

First time poster here...

Can anyone help me identify the regiment of this ancestor ? Sorry for the poor quality of the photo, I have asked my family for a better image if possible, and will upload that if I get one.

His cap badge appears to be pentagon shaped ? I cannot even give a year for this photograph unfortunately, as it was not annotated. My assumption is that this is around the First World War.

He is also sporting collar badges (rather than arm or shoulder), are there particular regiments or countries that do this ?

Thanks in anticipation !