Is this ptosis or excess skin? (Photo)

You do not appear to have extra eyelid skin.  The hollowing on the left upper eyelid is often associated with ptosis, although you don't have significantly low eyelid position.  You may have mild ptosis on both sides.  Your best bet is to have an in-person oculoplastic evaluation.

Looks you don’t have a defined eyelid crease on the left side. This may be a sign of ptosis. You should have an evaluation by an Oculoplastic surgeon in your area. 
Thank you for your question. 

The appearance of asymmetry is because the crease in your left upper eyelid is higher than the right. The actual heights of the eyelid margins (where the eyelashes are) appears to be symmetric so there may be very mild bilateral ptosis. As suggested, an exam by an oculopastic specialist may be helpful.

Thank you very much for the photo. It would be really helpful to see another photo go you looking straight ahead. To me the downgaze photo you published seems to show even upper eyelid height but a difference in the skin crease height. It also suggests that you have quite big eyes and a relatively small under eye cheek bone.Ideally you require an oculoplastic assessment. On first appearance there is no ptosis but the only way to find out is examination and measurements.