There are a lot of good pictures of many different species of plants, unfortunately most of the time you need to know what you are looking for to find them. Now then, a "weed" is simply a plant that you do not want growing where you do not want if to grow. So, in some instances, a rose could be a "weed", and I have those, roses growing where I do not want them becasue a neighbor planted a "rugosa" severalyears ago and the hips that get eaten by the birds get spread around all over and many do germinate and grow.
So, if you determine this plant is not what you wnat growing where you do not want it is is a "weed" and you can get rid of it.
Keep in mind also that many of those "weeds" can also be food plants and some of the plants people do want can be poisonous to us.

This forum's specialty is weeds, but you can post here or, especially for ornamental plants, try the Name That Plant forum.
As to posting a picture with limited hassle, an easy way is to open a free account at Photobucket.com. Upload your pictures there. Click on the HTML line (third line beneath your picture in Photobucket when you hold the cursor over your picture) and it should say "copied", then paste here [this gardenweb forum] in the message area - not in a link [You can paste multiple pictures regardless of size and you won't see the picture, but only computer lingo until you click on "Preview Message" below]. You will be able to post pictures on any other forum, too. After pasting your photos here [this gardenweb forum], you should see them when you hit "Preview Message" before you actually post the message.
hortster