图片放在 DCIM/100MYCAM 文件夹里，图片文件名也改成 IMG_0001 格式看看。

https://discussions.apple.com/thread/252518922 这里有人回复过：

Requirements for importing photos from a USB flash drive into the Photos app on an iPad or iPhone

The USB flash drive must contain a DCIM folder and another folder inside of that folder which is where the image files must be located. I named the subfolder 100NCD90 which was the name of a subfolder on a camera SD card I had.
It appears that any 8-character name will work as long as the first three characters are numbers. For example,
100AAAAA works.

The image file extension must be jpg, not jpeg.

The file name needs to be 8 characters with the last 4 being numbers. The first 4 can be numbers or letters or underscore. For example, DSC_0001 and IMGP0001 both work.