Graphic Designer for 3d Logo

I have a tiktok channel where I do “niche” content using many different “memoji” faces. I want to use one or more of my memoji faces and make a vector file and maybe a file I can use that is not vector but high quality to add to shirts, mugs etc on an online Merch store. Since I have to use the iPhone to create each memoji face I have taken screen shots of the faces and, within a photo editor, cropped out the background so it is just the face. I tried to apply that photo to the Merch store and it works but it is pixilated. I wanted to know if there is a way to get the “exact” same look but in a higher quality format? I can attach a few I have done l, that “may” need to be done in a higher quality but not sure where to start. I don’t want a “different” look. Just looking for exact match but higher quality. Thoughts?