I have a python app that I'd like to call on some images, by something like this:

right clicking on images in windows
menu pops up => shows the python application in the list of items
when clicked, batch runs on the images

Can this be done w/o using Visual Studio?
That "list of items" is called the context menu. That is controlled by "The Registry", which is only accessible by the computer's administrator.
MANDATORY WARNING: THE REGISTRY IS NOT A TOY, AND WILL BREAK YOUR COMPUTER IF YOU DO NOT KNOW WHAT YOU ARE DOING. IF YOU ARE NOT AT LEAST 80% CONFIDENT, DON'T TOUCH IT. I TAKE NO RESPONSIBILITY IF YOU BREAK YOUR COMPUTER. 
That's not to say you will though. If you still want to continue, you should definitely back it up: 

Open the registry


Press (Windows key) + R to open the run dialog
Type in "regedit.exe" and then enter
Enter you Administrative approval when prompted

Once in the registry, look at the panel on the left and all the way at the top there should be a "folder" (called "key" in the registry) called "HKEY_CLASSES_ROOT". Click on it. (If you can't find it, it might be under "Computer". Just expand it.). You should now see a lot of keys.
Backup the registry (optional but recommended)

Click on "File" (top) => "Export". 
On the bottom, choose "Selected branch". If you want though, you could export the whole registry by selecting "All" just to be safe (it's a HUGE file though, and probably not necessary)
Choose a file to save it to and click "Save". Wait for the loading to finish.

Decide which file type you want. You said: image. That could be: ".jpg", ".png", ".bmp", etc. Just repeat the following steps for all desired file types.
Find the "file type association"


Under your selected key, find the key with the file extension you want (eg. ".jpg"). Click on it 
There will be a couple of "values" on the side. Check the one called "(Default)". This has the name of the file. (eg: "jpegfile")

Navigate to the file. Still in the same key as the extension (".jpg"), locate the key with the name from step 5. Open it.
Make a new command.


Right-Click the "shell" key, select "New" => "key"
Name this new key with a logical, one word name (eg "process").
This new key has a "(Default") value. Change it's value (not the name) to what you want to appear on the right click menu. 
Under your new key, make a new key called "command".
Set this key's default value to the full path of your Python installation, a space, then the script path, including any arguments. You can pass "%L%" as an argument to have the registry replace it with the path to the right-clicked file. (eg. "path/to/python.exe path/to/script.py %L%"). Just  make sure your Python script can take arguments.


Done!
Feel free to comment with questions
Is there a way to invoke python from Windows click?