Photo tagging/keyword software

So I have around 15,000 pictures of documents for my PhD that I need to go through and analyse. For future reference, I need to tag each picture with suitable keywords, so that I don't need to slug through all of them. My supervisor was useless and just told me to make an excel table - which would be horrendously cumbersome and slow. So I thought of Picasa, and it works pretty well. However, since I don't have enough room on my laptop for all of them, some are stored on my Skydrive and others on my Google Drive. I haven't found a way to let Picasa go through those.

Is my only option to buy an external HDD and only then use Picasa? Also, does anyone know if there are scripts/macros for keyword input so I wouldn't have to write them each time?

At least there's a way to map SkyDrive as a network drive, maybe you can set that as a drive on your compy and tell Picasa to scan that drive for photos. Will take a good amount of bandwidth though, I'd presume. So prepare for that.

**** it, I ended up ordering a 1 TB external drive. Going to take few hours to move stuff over that but then I don't have to worry about bandwidth. Or running out of space ever again.

Probably the better choice as long as you make sure to prevent any damage befalling it.