To add an image title, simply double-click on a photo in Stacks edit mode. Double-clicking will bring up the Image Edit mode in Stacks. From here, you’ll be able to add or edit the image ALT tag. The ALT tag (ALT is an abbreviation for alternative text) is used as the title, for the image shown in Photo Album Pro.

It’s also recommended you give the images a basic file name. This can be beneficial to search engines indexing your website.
When you have finished editing the image details, click on the blue Done button, at the top left.