Alternative:
Currently, Obsidian has horrible or non-existent Find and Replace. But since these are just text files in an OS folder, you can use something like Notepad++ to search and replace across multiple files within your vault or even a single folder in the vault.
All you really need to do is replace “<img width=“300” height=“300” src=”…/_resources/" with “![[”, and replace “”/>" with “]]”. Assuming the images had all the same size parameters.
Obsidian uses ![[image_name.extension]] for the internal link to images with that name in your designated attachment folder.
That second replacement could be tricky because you might have "/> in other files and you don’t want to screw those up. I might suggest you practice with the multi file replacement in a single folder first and back up your vault before you do any of this.
Idea, for the second replacement, assuming your images are png files for example, you could replace “.png”/>" with “.png]]” to avoid accidentally matching other patterns of "/>.
Notepad++ is simple, but a wrong key and you could really mess up your vault.
I tested it on your exact string in two of my notes and it worked fine.
I didn’t test if the link would connect to images after it was created. I think you should test that first.
I closed Obsidian before I did the Notepad replacement.
In Notepad++,
Search>
Find in Files>
Find what
Replace with
Directory
Back up first.