I'm assuming you have a point layer, with a photo URL specified in an attribute for each point, and want to display that photo at the respective point in the map.
In the symbology for that layer, make it Single Symbol with a Raster Image Marker as the symbol layer type. Underneath, where you would expect to specify the path of a single image to use for all point, instead at the right choose Data Driven Override, and specify the attribute with the URL as the variable. I believe for some time now this would work if the field contained a (fully qualified) local filename to the photo, but I have just tested and in QGIS 3.6 it allows also a remote URL, not only a filename.
You'll need to set an appropriate symbol size, in display or map units. Here it's 10mm. The bottom 2 photos are local files on my harddrive, the top one a web image via URL.
If your attribute is not a fully qualified URL or filename, you can use the expression editor in the data driven override to add a prefix as necessary, etc., eg.
'c:\\pathname\\'+"Photo Name" or
'http://website/'+"Photo Name" (note the doubled backslashes to escape them).