Alpha channel not supported: /home/9/7/5/23608/23608/public_html/moodle/mod/certificate/pix/signatures/mersig.png.
I have a jpg version of the file as well in the folder and it doesn't even show up as an option to select even though the Help item for it says jpg is supported.
My custom seal/logo works fine.
I'm using 1.9.3+ and uploaded a new seal/logo image both as a png and jpg. However they do not show up as an option in the seal/log list. Did you ever get the signatures to show up as an option?
I've been searching for a solution and so far have not found one.
Okay. I finally figured out what I was doing wrong.
I saved the file as a png, but did not remove the transparency or save it as png 8. My mistake and other than this it works great!
Hope this will help someone else.