How do I choose a font size to exactly fit a string in a given rectangle?

[subhendu]

I have a background image (the size of this image can change), and I need to put some text in this piece of image. Depending upon the background image, the font size needs to be adjusted.

Thanks.

[Weedpacket]

Pick a small font size, and use [man]imagettfbox[/max] to see how big a box it needs. If it can fit within the bounds of the rectangle, increase the size a bit and try again. Repeat until it gets too big to fit, then go back down one step and that's the size you want.