On some screens, the image obscures the welcome text.
Also, the edge of the image is visible vis-a-vis the drop shadow on the text being cut off, though this is actually a dimensional issue not specific to alpha.
Neither of these are usability issues; purely aesthetic.
I can help convert the image to one with a proper alpha channel if need be, though I suspect there is a photoshop file or similar that would make that fairly painless.
Also, the edge of the image is visible vis-a-vis the drop shadow on the text being cut off, though this is actually a dimensional issue not specific to alpha.
Neither of these are usability issues; purely aesthetic.
I can help convert the image to one with a proper alpha channel if need be, though I suspect there is a photoshop file or similar that would make that fairly painless.