Based on your description of the image, it involves a cell membrane and a circular vesicle. This likely indicates the process of endocytosis, as this process involves the cell membrane engulfing material and forming a vesicle to bring substances into the cell.
Endocytosis is characterized by the membrane folding inward to create a vesicle, which is consistent with your mention of a "circular vesicle."
So, the answer is:
endocytosis.