I am a photographer and was concerned about the same. I checked out the database and found that it only contains three tables:
- One for gallery information,
- One for the gallery images,
- One for the general settings.
The second, the gallery images, only contains text and integer fields--no binary fields that could contain images. Therefore, each additional image (record) would only take about 2k (kilobytes) of space in the database itself.
The actual images, in all sizes, are stored within the site structure itself as files (not the database) within the PowerGallery folder. In whatever folder you installed PowerGallery, there is another folder called "images". Inside the "images" folder there are numbered folders (1, 2, 3...) for each gallery. That is where your space will get used.
In my gallery folders (the numerical ones) there are nine (9) copies of each image, at differing sizes (thumbnail, 1024px wide, etc.) including the original image. As far as total size is concerned, here is what my site is showing:
Typical original size (all my images are presized to 1500px on the longest size): 300K
Eight other PG sized/watermarked images: 250K total all eight.
Hope that helps...