Try this:
Code: Select all
convert ( -size 500x50 xc:rgba(255,255,8,0.5) -font /font/arial.ttf -fill rgba(0,0,0,1) -pointsize 42 -gravity center -annotate +0+0 "This is my label!" ) input.jpg +swap -gravity SouthEast -geometry +0+20 -composite output.jpg
This creates a canvas first using a semi transparent rgb colour; the brackets hold this information together - might work without but it is easier to see what is happening.
The -geometry moves the watermark up from the bottom by 20 pixels.
I belive label fits the background to the text and that is why I made a canvas first; so you can have some space around the text. This can have complications if your text size changes.
Imagemagick has so many options it can be hard to work things out until you start to see how it works. You can check out
Anthony's examples and I have a few on my site using php.