In your screen shot, any differences in resolution are difficult to see even when I zoom in. But what's obvious is an apparent loss of transparency in the left hand example. This may happen if this graphic is in a field and it get's the focus (click on or tab into the field). There may also be a visible change in some layouts if the current record has been opened for editing.
Is this a graphic that was inserted into a field?
I just copied and pasted the graphic onto the layout.