PictPress needs either the ImageMagick convert program or the GD2 library to resize images.
PictPress optionally uses exif_read_data or the rdjpgcom program to read comments from the images.; exif_read_data is also optionally used to read EXIF data like picture date etc.
You will need some other means to upload images to subdirectories of the WordPress upload directory.
Unzip pictpress.zip in the plugin directory of your WordPress site. This creates a pictpress directory plus a pictpress.php file.
Go to the Plugin admin page and press the install/upgrade link.
Enable the PictPress plugin on the Plugins admin page.
Make sure that you have configured a valid destination directory for Uploads under Options >> Miscellaneous and that the web server has write access to the upload directory.