If you try to convert a PSD image with layers to a web format like PNG using ImageMagick, you’ll get a PNG image for each layer and that’s probably not what you want.

Here’s the -flatten option that helps you:

find . -name *.psd -exec convert '{}' -flatten \
`basename '{}' .psd`.png \;

Et voilà. A bunch of PSD images ready for uploading into MediaWiki using PyWikipediaBot.