I can only seem to get phpThumbOf to work when supplying it with an absolute file path from the root of the hard disk like so:
/var/www/modx2/assets/images/filename.jpg
When the value of the image template variable is
assets/images/filename.jpg, this works:
[[phpthumbof? &input=`/var/www/modx2/[[+tv.feature-image]]` &options=`&w=277`]]
But this does not:
[[phpthumbof? &input=`[[+tv.feature-image]]` &options=`&w=277`]]
Which just seems absurd.
My solution was to ditch phpThumbOf, phpThumbsUp etc and install
pThumb, which worked out of the box!