how to change all pics caption and tag in one time?

You can use the Settings/Media Library Assistant IPTC/EXIF tab to compose values for captions and tags and map all of your Media Library Items at one time. On the Settings/Media Library Assistant Documentation tab, look for the “IPTC & EXIF Processing Options” section to see how to do this.

The “EXIF/Template mapping with Content Templates” section of the Documentation tells how to use Content Templates to compose caption and tag values from a wide range of sources, not just IPTC and EXIF metadata.

I hope that gets you started on using the mapping rules to automate your process. I’m going to mark this topic resolved, but feel free to update it if you have any problems or further questions. Thanks for your interest in the plugin.

Thanks, but it is too complicated for me to understand
could you explain more? for example, I have 10 pics in my media library now and want to add caption and tag.
1)I go “IPTC & EXIF Processing Options”
2)in “Standard field mapping”, we have “Field Title IPTC Value EXIF/Template Value Priority Existing Text”, so how do I select for each of them? where I should write the caption and tags?
ideally I hope I can write a fixed “***” for the caption and tags for all pics.

You can write a fixed “***” value for the caption field with these steps:

1. Go to the Settings/Media Library Assistant IPTC/EXIF tab
2. Enter template:*** in the EXIF/Template Value textbox on the Standard field mapping line for the Caption field
3. Scroll down to the bottom of the screen and click “Save Changes” to save your rule
4. When the screen refreshes, click the “Map All Attachments, Standard Fields Now” to apply the rule.

You can also put more meaningful values in the caption by entering templates such as template:[+file_name+] or template:[+title+].

The same steps will work for the “Tags” line in the Taxonomy term mapping section of the screen.

If you check the “Enable IPTC/EXIF Mapping when adding new media” box at the top of the screen, the rule will be applied automatically to any pictures added later; you will not have to re-apply the rule manually.