narrowing it down, this works
cat /etc/tika/tika-server-config-custom.xml
<?xml version="1.0" encoding="UTF-8"?>
<properties>
<parsers>
</parsers>
<server>
<params>
...
but this doesn't,
cat /etc/tika/tika-server-config-custom.xml
<?xml version="1.0" encoding="UTF-8"?>
<properties>
<parsers>
+ <parser
class="org.apache.tika.parser.ocr.TesseractOCRParser">
+ </parser>
</parsers>
<server>
<params>
...
checking tika source, that appears to be the right path,
find . | grep /TesseractOCRParser.class
./org/apache/tika/parser/ocr/TesseractOCRParser.class
:-/