Most probable reason is that you have mod_security module enabled

Check your firebug console for the error while uploading photos, I believe you will see Forbidden error there. 

And, please, do the search before posting anything on the forum: http://www.oxwall.org/forum/topic/21910?&page=2

Thank you for your answer.

I'm sorry but I don't think the solution is around mod_security module. After disabled it the problem remains.

However, I have a new element. All works fine when we create a new Album or when adding photos into a new album. Then, we have an address like this:
http://xxxx.xx/ox/photo/useralbum/xxxxx/5

But if the address is the one we get when we click on Photos button (http://xxxx.xx/ox/photo/viewlist/latest), we can't upload and no error is reported.

check folder permissions 
if not right image not get uploadeed

Can you please share your URL? make sure website is open for registration. 

Hi,

Thank you.

The site URL is:

http://jbrum.pt/ox

The mod security module is still enabled as I get Forbidden error in the console. See screenshot in the attachment

Hi,

Security module is disabled and it works fine.
Thank you.

By working fine you mean you can upload photos now? Please confirm

Drag & Drop - always error message: timeout
Click to browse - we can upload photos

I'm sorry but I just tried drag and drop on your website and everything works just fine: http://jbrum.pt/ox/photo/useralbum/tester/6

I can't reproduce the timeout issue on your website

A 5Mb file is uploaded, a 20Mb -> timeout

If the image is too big and it can't be upload within 60 seconds due to the slow internet connection or probably hosting capacities, you get the timeout

You can increase the timeout period, however you will need to tweak the server setting as well, that can cause additional load on your server. 

In order to do that go here: 

ow_plugins/photo/static/js/upload.js

line 325

increase the value 

timeout: 60000,

then go to your php.ini file and increase the value for these directives: 

max_execution_time and max_input_time, but don't make it too big otherwise you will overload your server. 

Also, this change will be overwritten while next update of the photo plugin

I can't upload - via normal upload - a 20Mb file size, BUT it can be uploaded in a post. (!!!)

I didn't change the timeout nor create a php.ini

There's different functional for uploading photos in the post and in the photo section

May be thinking about a new approach in the future...

Why do you need such a huge photo size anyway?

You are right. The photo - after uploaded - has no more the original size.
So we can think about reduce the original size into the uploaded size on the server.

Yes, we use GD library to process the images, which crops the images after uploading to decrease the load on the server

I use mod security with no issues.  I did however disable suhosin.